diff --git a/doc/#说明.md b/doc/#说明.md
new file mode 100644
index 0000000..601d3fa
--- /dev/null
+++ b/doc/#说明.md
@@ -0,0 +1,23 @@
+#说明
+
+##Windows环境编译步骤
+
+1.打开命令提示符（cmd)
+
+2.进入项目src文件夹
+
+3.执行以下命令：
+
+chcp 65001
+
+javac *.java
+
+##注意事项
+
+1.chcp 65001 命令用于设置控制台编码为 UTF-8，确保中文正常显示
+
+2.必须在执行编译命令前设置编码
+
+##运行程序
+
+java Main
\ No newline at end of file
diff --git a/src/AccountManager.java b/src/AccountManager.java
index cb26a91..b6f4d72 100644
--- a/src/AccountManager.java
+++ b/src/AccountManager.java
@@ -1,37 +1,37 @@
-import java.util.HashMap;
-import java.util.Map;
+import java.util.ArrayList;
+import java.util.List;
 
 
 public class AccountManager {
-    private Map<String, User> users;
+    private List<User> users;
     
     public AccountManager() {
         initializeUsers();
     }
     
     private void initializeUsers() {
-        users = new HashMap<>();
+        users = new ArrayList<>();
         
-        addUser("张三1", "123", UserType.PRIMARY);
-        addUser("张三2", "123", UserType.PRIMARY);
-        addUser("张三3", "123", UserType.PRIMARY);
+        users.add(new User("张三1", "123", UserType.PRIMARY));
+        users.add(new User("张三2", "123", UserType.PRIMARY));
+        users.add(new User("张三3", "123", UserType.PRIMARY));
         
-        addUser("李四1", "123", UserType.JUNIOR);
-        addUser("李四2", "123", UserType.JUNIOR);
-        addUser("李四3", "123", UserType.JUNIOR);
+        users.add(new User("李四1", "123", UserType.JUNIOR));
+        users.add(new User("李四2", "123", UserType.JUNIOR));
+        users.add(new User("李四3", "123", UserType.JUNIOR));
         
-        addUser("王五1", "123", UserType.SENIOR);
-        addUser("王五2", "123", UserType.SENIOR);
-        addUser("王五3", "123", UserType.SENIOR);
-    }
-    
-    private void addUser(String username, String password, UserType type) {
-        users.put(username + ":" + password, new User(username, password, type));
+        users.add(new User("王五1", "123", UserType.SENIOR));
+        users.add(new User("王五2", "123", UserType.SENIOR));
+        users.add(new User("王五3", "123", UserType.SENIOR));
     }
     
     public User authenticate(String username, String password) {
-        String key = username + ":" + password;
-        return users.get(key);
+        for (User user : users) {
+            if (user.getUsername().equals(username) && user.getPassword().equals(password)) {
+                return user;
+            }
+        }
+        return null;
     }
     
     public boolean isValidUserType(String typeName) {
diff --git a/src/Filemanager.java b/src/Filemanager.java
index c1e0461..f05aaac 100644
--- a/src/Filemanager.java
+++ b/src/Filemanager.java
@@ -60,27 +60,16 @@ public class Filemanager {
         for (File file : files) {
             try (BufferedReader reader = new BufferedReader(new FileReader(file))) {
                 String line;
-                StringBuilder question = new StringBuilder();
-                boolean inQuestion = false;
-                
                 while ((line = reader.readLine()) != null) {
+                    line = line.trim();
+                    if (line.isEmpty()) continue;
+                    
+                    // 提取题目内容（去除题号）
                     if (line.matches("^\\d+\\.\\s.*")) {
-                        if (inQuestion) {
-                            allQuestions.add(question.toString().trim());
-                            question.setLength(0);
-                        }
-                        String questionContent = line.substring(line.indexOf(". ") + 2);
-                        question.append(questionContent);
-                        inQuestion = true;
-                    } else if (inQuestion && !line.trim().isEmpty()) {
-                        question.append(" ").append(line.trim());
+                        String question = line.substring(line.indexOf(". ") + 2).trim();
+                        allQuestions.add(question);
                     }
                 }
-                
-                if (inQuestion && question.length() > 0) {
-                    allQuestions.add(question.toString().trim());
-                }
-                
             } catch (IOException e) {
                 System.err.println("读取文件失败: " + file.getName());
             }
@@ -88,4 +77,25 @@ public class Filemanager {
         
         return allQuestions;
     }
+    
+ 
+    public void clearUserHistory(String username) {
+        String userDirPath = BASE_DIR + File.separator + username;
+        File userDir = new File(userDirPath);
+        
+        if (userDir.exists() && userDir.isDirectory()) {
+            File[] files = userDir.listFiles();
+            if (files != null) {
+                int count = 0;
+                for (File file : files) {
+                    if (file.delete()) {
+                        count++;
+                    }
+                }
+                System.out.println("已删除 " + count + " 个历史文件");
+            }
+        } else {
+            System.out.println("没有找到历史文件");
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/Main.java b/src/Main.java
index bad3bb0..a42fa04 100644
--- a/src/Main.java
+++ b/src/Main.java
@@ -1,6 +1,5 @@
 import java.util.Scanner;
 
-
 public class Main {
     private AccountManager accountManager;
     private PaperGenerator paperGenerator;
@@ -84,8 +83,10 @@ public class Main {
                     continue;
                 }
                 
+                System.out.println("正在生成试卷，请稍候...");
                 String[] questions = paperGenerator.generatePaper(questionCount, fileManager);
                 fileManager.savePaper(currentUser.getUsername(), questions);
+                System.out.println("试卷生成成功！");
                 
             } catch (NumberFormatException e) {
                 System.out.println("请输入有效的数字（10-30或-1）");
@@ -118,7 +119,6 @@ public class Main {
             app.run();
         } catch (Exception e) {
             System.err.println("程序出现异常: " + e.getMessage());
-            e.printStackTrace();
         }
     }
 }
\ No newline at end of file
diff --git a/src/PaperGenerator.java b/src/PaperGenerator.java
index 604c6da..71803ab 100644
--- a/src/PaperGenerator.java
+++ b/src/PaperGenerator.java
@@ -1,16 +1,17 @@
 import java.util.HashSet;
+import java.util.Random;
 import java.util.Set;
 
 
 public class PaperGenerator {
     private IQuestionGenerator questionGenerator;
-    private Set<String> generatedQuestions;
     private User currentUser;
+    private Random random;
     
     public PaperGenerator(User user) {
         this.currentUser = user;
         this.questionGenerator = QuestionGeneratorFactory.createGenerator(user.getUserType());
-        this.generatedQuestions = new HashSet<>();
+        this.random = new Random();
     }
     
     public void setUserType(UserType userType) {
@@ -22,27 +23,99 @@ public class PaperGenerator {
             throw new IllegalArgumentException("题目数量必须在10-30之间");
         }
         
-        String[] questions = new String[questionCount];
         Set<String> allHistoryQuestions = fileManager.loadAllQuestions(currentUser.getUsername());
-        generatedQuestions.addAll(allHistoryQuestions);
+        System.out.println("历史题目数量: " + allHistoryQuestions.size());
+        
+        String[] questions = new String[questionCount];
+        Set<String> usedQuestions = new HashSet<>();
         
         for (int i = 0; i < questionCount; i++) {
             String question;
             int attempt = 0;
-            int maxAttempts = 100; 
+            int maxAttempts = 500; 
             
             do {
                 question = questionGenerator.generateQuestion();
                 attempt++;
+                
+                if (attempt > 100) {
+                    question = generateSimpleQuestion();
+                }
+                
                 if (attempt >= maxAttempts) {
-                    throw new RuntimeException("无法生成不重复的题目，请尝试清理历史文件");
+                    System.out.println("警告：第 " + (i+1) + " 题尝试次数过多，使用备用题目");
+                    question = generateFallbackQuestion();
+                    break;
                 }
-            } while (generatedQuestions.contains(question) || !questionGenerator.isValidQuestion(question));
+                
+            } while (allHistoryQuestions.contains(question) || 
+                     usedQuestions.contains(question) || 
+                     !questionGenerator.isValidQuestion(question));
             
-            generatedQuestions.add(question);
+            usedQuestions.add(question);
             questions[i] = (i + 1) + ". " + question;
+            System.out.println("成功生成第 " + (i+1) + " 题");
         }
         
         return questions;
     }
+    
+
+    private String generateSimpleQuestion() {
+        switch (currentUser.getUserType()) {
+            case PRIMARY:
+                return generateSimplePrimaryQuestion();
+            case JUNIOR:
+                return generateSimpleJuniorQuestion();
+            case SENIOR:
+                return generateSimpleSeniorQuestion();
+            default:
+                return generateSimplePrimaryQuestion();
+        }
+    }
+    
+    private String generateSimplePrimaryQuestion() {
+        int a = random.nextInt(100) + 1;
+        int b = random.nextInt(100) + 1;
+        String[] ops = {"+", "-", "*", "/"};
+        String op = ops[random.nextInt(ops.length)];
+        return a + " " + op + " " + b + " = ";
+    }
+    
+    private String generateSimpleJuniorQuestion() {
+        int a = random.nextInt(100) + 1;
+        int b = random.nextInt(100) + 1;
+        String[] ops = {"+", "-", "*", "/"};
+        String op = ops[random.nextInt(ops.length)];
+        
+        if (random.nextBoolean()) {
+            return "√" + a + " " + op + " " + b + " = ";
+        } else {
+            return a + "² " + op + " " + b + " = ";
+        }
+    }
+    
+    private String generateSimpleSeniorQuestion() {
+        int a = random.nextInt(100) + 1;
+        int angle = random.nextInt(360) + 1;
+        String[] ops = {"+", "-", "*", "/"};
+        String op = ops[random.nextInt(ops.length)];
+        String[] trig = {"sin", "cos", "tan"};
+        String trigFunc = trig[random.nextInt(trig.length)];
+        
+        return trigFunc + "(" + angle + "°) " + op + " " + a + " = ";
+    }
+    
+    private String generateFallbackQuestion() {
+        switch (currentUser.getUserType()) {
+            case PRIMARY:
+                return (random.nextInt(100) + 1) + " + " + (random.nextInt(100) + 1) + " = ";
+            case JUNIOR:
+                return "√" + (random.nextInt(100) + 1) + " + " + (random.nextInt(100) + 1) + " = ";
+            case SENIOR:
+                return "sin(" + (random.nextInt(360) + 1) + "°) + " + (random.nextInt(100) + 1) + " = ";
+            default:
+                return (random.nextInt(100) + 1) + " + " + (random.nextInt(100) + 1) + " = ";
+        }
+    }
 }
\ No newline at end of file
diff --git a/src/QuestionGenerator.java b/src/QuestionGenerator.java
index b24762d..9579bc6 100644
--- a/src/QuestionGenerator.java
+++ b/src/QuestionGenerator.java
@@ -1,123 +1,102 @@
 import java.util.Random;
 
-
 interface IQuestionGenerator {
     String generateQuestion();
     boolean isValidQuestion(String question);
 }
 
-
 class PrimaryQuestionGenerator implements IQuestionGenerator {
     private Random random = new Random();
     private String[] operators = {"+", "-", "*", "/"};
     
     @Override
     public String generateQuestion() {
-        int operandCount = random.nextInt(3) + 2; 
-        StringBuilder question = new StringBuilder();
-        
-        question.append(random.nextInt(100) + 1);
-        
-        for (int i = 1; i < operandCount; i++) {
-            String operator = operators[random.nextInt(operators.length)];
-            int operand = random.nextInt(100) + 1;
+        try {
+            int operandCount = random.nextInt(3) + 2; 
+            StringBuilder question = new StringBuilder();
             
-            if (random.nextBoolean() && i < operandCount - 1) {
-                question.append(" ").append(operator).append(" (").append(operand);
-                if (random.nextBoolean()) {
-                    question.append(" ").append(operators[random.nextInt(operators.length)])
-                           .append(" ").append(random.nextInt(100) + 1).append(")");
-                    i++;
-                }
-            } else {
+            question.append(random.nextInt(100) + 1);
+            
+            for (int i = 1; i < operandCount; i++) {
+                String operator = operators[random.nextInt(operators.length)];
+                int operand = random.nextInt(100) + 1;
                 question.append(" ").append(operator).append(" ").append(operand);
             }
+            
+            return question.toString() + " = ";
+        } catch (Exception e) {
+            return (random.nextInt(100) + 1) + " + " + (random.nextInt(100) + 1) + " = ";
         }
-        
-        String result = question.toString();
-        int openCount = countChar(result, '(');
-        int closeCount = countChar(result, ')');
-        while (openCount > closeCount) {
-            result += ")";
-            closeCount++;
-        }
-        
-        return result + " = ";
     }
     
     @Override
     public boolean isValidQuestion(String question) {
-        return question.matches("^[0-9+\\-*/().\\s]+=$") && 
-               !question.contains("²") && !question.contains("√") &&
-               !question.contains("sin") && !question.contains("cos") && !question.contains("tan");
-    }
-    
-    private int countChar(String str, char ch) {
-        int count = 0;
-        for (char c : str.toCharArray()) {
-            if (c == ch) count++;
+        try {
+            return question != null && 
+                   question.contains("=") && 
+                   !question.contains("²") && 
+                   !question.contains("√") &&
+                   !question.contains("sin") && 
+                   !question.contains("cos") && 
+                   !question.contains("tan");
+        } catch (Exception e) {
+            return false;
         }
-        return count;
     }
 }
 
-
 class JuniorQuestionGenerator implements IQuestionGenerator {
     private Random random = new Random();
     private String[] operators = {"+", "-", "*", "/"};
     
     @Override
     public String generateQuestion() {
-        StringBuilder question = new StringBuilder();
-        int operandCount = random.nextInt(3) + 2; 
-        boolean hasSpecialOperator = false;
-        
-        question.append(random.nextInt(100) + 1);
-        
-        for (int i = 1; i < operandCount; i++) {
-            String operator;
-            if (!hasSpecialOperator && random.nextDouble() < 0.4) {
-                if (random.nextBoolean()) {
-                    operator = "²";
-                    hasSpecialOperator = true;
-                } else {
-                    operator = "√";
-                    hasSpecialOperator = true;
-                }
-            } else {
-                operator = operators[random.nextInt(operators.length)];
-            }
+        try {
+            StringBuilder question = new StringBuilder();
             
-            int operand = random.nextInt(100) + 1;
-            
-            if (operator.equals("²")) {
-                question.append("²");
-            } else if (operator.equals("√")) {
-                question.append(" ").append(operator).append(operand);
-            } else {
-                question.append(" ").append(operator).append(" ").append(operand);
-            }
-        }
-        
-        if (!hasSpecialOperator) {
             if (random.nextBoolean()) {
-                question.append("²");
+                question.append("√").append(random.nextInt(100) + 1);
             } else {
-                question.append(" √").append(random.nextInt(100) + 1);
+                question.append(random.nextInt(100) + 1).append("²");
             }
+            
+            int extraOps = random.nextInt(2) + 1;
+            for (int i = 0; i < extraOps; i++) {
+                String operator = operators[random.nextInt(operators.length)];
+                int operand = random.nextInt(100) + 1;
+                
+                if (random.nextDouble() < 0.3) {
+                    if (random.nextBoolean()) {
+                        question.append(" ").append(operator).append(" √").append(operand);
+                    } else {
+                        question.append(" ").append(operator).append(" ").append(operand).append("²");
+                    }
+                } else {
+                    question.append(" ").append(operator).append(" ").append(operand);
+                }
+            }
+            
+            return question.toString() + " = ";
+        } catch (Exception e) {
+            return "√1 + 1 = ";
         }
-        
-        return question.toString() + " = ";
     }
     
     @Override
     public boolean isValidQuestion(String question) {
-        return (question.contains("²") || question.contains("√")) &&
-               !question.contains("sin") && !question.contains("cos") && !question.contains("tan");
+        try {
+            return question != null && 
+                   question.contains("=") && 
+                   (question.contains("²") || question.contains("√")) &&
+                   !question.contains("sin") && 
+                   !question.contains("cos") && 
+                   !question.contains("tan");
+        } catch (Exception e) {
+            return false;
+        }
     }
 }
 
-
 class SeniorQuestionGenerator implements IQuestionGenerator {
     private Random random = new Random();
     private String[] operators = {"+", "-", "*", "/"};
@@ -125,50 +104,44 @@ class SeniorQuestionGenerator implements IQuestionGenerator {
     
     @Override
     public String generateQuestion() {
-        StringBuilder question = new StringBuilder();
-        int operandCount = random.nextInt(3) + 2; 
-        boolean hasTrigFunction = false;
-        
-        if (random.nextDouble() < 0.6) {
+        try {
+            StringBuilder question = new StringBuilder();
+            
             String trigFunc = trigFunctions[random.nextInt(trigFunctions.length)];
-            int angle = random.nextInt(360) + 1;
-            question.append(trigFunc).append("(").append(angle).append("°)");
-            hasTrigFunction = true;
-        } else {
-            question.append(random.nextInt(100) + 1);
-        }
-        
-        for (int i = 1; i < operandCount; i++) {
-            String operator = operators[random.nextInt(operators.length)];
+            question.append(trigFunc).append("(").append(random.nextInt(360) + 1).append("°)");
             
-            if (!hasTrigFunction && random.nextDouble() < 0.5) {
-                String trigFunc = trigFunctions[random.nextInt(trigFunctions.length)];
-                int angle = random.nextInt(360) + 1;
-                question.append(" ").append(operator).append(" ").append(trigFunc).append("(").append(angle).append("°)");
-                hasTrigFunction = true;
-            } else {
-                int operand = random.nextInt(100) + 1;
-                question.append(" ").append(operator).append(" ").append(operand);
+            int extraOps = random.nextInt(2) + 1;
+            for (int i = 0; i < extraOps; i++) {
+                String operator = operators[random.nextInt(operators.length)];
+                
+                if (random.nextDouble() < 0.4) {
+                    trigFunc = trigFunctions[random.nextInt(trigFunctions.length)];
+                    question.append(" ").append(operator).append(" ").append(trigFunc)
+                           .append("(").append(random.nextInt(360) + 1).append("°)");
+                } else {
+                    int operand = random.nextInt(100) + 1;
+                    question.append(" ").append(operator).append(" ").append(operand);
+                }
             }
+            
+            return question.toString() + " = ";
+        } catch (Exception e) {
+            return "sin(45°) + 1 = ";
         }
-        
-        if (!hasTrigFunction) {
-            String trigFunc = trigFunctions[random.nextInt(trigFunctions.length)];
-            int angle = random.nextInt(360) + 1;
-            question.append(" ").append(operators[random.nextInt(operators.length)])
-                   .append(" ").append(trigFunc).append("(").append(angle).append("°)");
-        }
-        
-        return question.toString() + " = ";
     }
     
     @Override
     public boolean isValidQuestion(String question) {
-        return question.contains("sin") || question.contains("cos") || question.contains("tan");
+        try {
+            return question != null && 
+                   question.contains("=") && 
+                   (question.contains("sin") || question.contains("cos") || question.contains("tan"));
+        } catch (Exception e) {
+            return false;
+        }
     }
 }
 
-
 class QuestionGeneratorFactory {
     public static IQuestionGenerator createGenerator(UserType userType) {
         switch (userType) {
diff --git a/src/数学试卷/张三1/2025-09-29-09-37-51.txt b/src/数学试卷/张三1/2025-09-29-09-37-51.txt
new file mode 100644
index 0000000..f479d3c
--- /dev/null
+++ b/src/数学试卷/张三1/2025-09-29-09-37-51.txt
@@ -0,0 +1,19 @@
+1. 19 - 21 = 
+
+2. 38 * 82 - 34 - 22 = 
+
+3. 46 * 34 * 47 = 
+
+4. 23 + 38 / 49 - 19 = 
+
+5. 76 - 62 / 48 + 52 = 
+
+6. 40 * 78 * 27 * 10 = 
+
+7. 17 / 44 - 89 = 
+
+8. 53 + 68 = 
+
+9. 54 / 41 = 
+
+10. 63 / 98 = 
diff --git a/src/数学试卷/张三1/2025-09-29-09-38-13.txt b/src/数学试卷/张三1/2025-09-29-09-38-13.txt
new file mode 100644
index 0000000..d40b855
--- /dev/null
+++ b/src/数学试卷/张三1/2025-09-29-09-38-13.txt
@@ -0,0 +1,59 @@
+1. 10 + 100 - 35 / 52 = 
+
+2. 11 * 4 / 55 = 
+
+3. 84 * 63 / 76 = 
+
+4. 55 - 51 = 
+
+5. 28 * 94 / 8 - 53 = 
+
+6. 25 - 3 + 97 * 84 = 
+
+7. 76 - 7 + 30 = 
+
+8. 58 - 80 = 
+
+9. 60 + 69 / 33 - 70 = 
+
+10. 69 * 59 / 70 + 80 = 
+
+11. 24 + 90 + 1 = 
+
+12. 95 / 18 = 
+
+13. 17 * 5 / 70 = 
+
+14. 87 + 16 - 74 * 10 = 
+
+15. 80 + 71 = 
+
+16. 100 * 72 = 
+
+17. 95 / 100 * 30 + 98 = 
+
+18. 51 + 60 = 
+
+19. 78 + 35 - 63 / 36 = 
+
+20. 89 / 22 = 
+
+21. 25 / 9 = 
+
+22. 13 * 87 + 92 * 29 = 
+
+23. 92 / 3 = 
+
+24. 20 * 21 - 72 = 
+
+25. 18 + 6 = 
+
+26. 56 / 23 = 
+
+27. 24 * 51 * 60 = 
+
+28. 73 + 34 / 92 = 
+
+29. 65 - 47 = 
+
+30. 48 / 52 + 51 / 20 = 
diff --git a/src/数学试卷/张三1/2025-09-29-09-39-05.txt b/src/数学试卷/张三1/2025-09-29-09-39-05.txt
new file mode 100644
index 0000000..e137ff3
--- /dev/null
+++ b/src/数学试卷/张三1/2025-09-29-09-39-05.txt
@@ -0,0 +1,39 @@
+1. tan(100°) / 14 - 87 = 
+
+2. cos(231°) - 55 * 14 = 
+
+3. sin(283°) / cos(56°) / 94 = 
+
+4. sin(6°) - 2 = 
+
+5. tan(69°) / 56 = 
+
+6. cos(272°) + 25 = 
+
+7. cos(211°) * 73 - 54 = 
+
+8. cos(337°) / 57 = 
+
+9. cos(282°) * cos(357°) = 
+
+10. tan(126°) + 84 = 
+
+11. cos(307°) - 7 = 
+
+12. cos(210°) / 60 = 
+
+13. sin(281°) / 44 = 
+
+14. sin(296°) + 23 = 
+
+15. cos(82°) * 96 = 
+
+16. tan(353°) - 12 * 84 = 
+
+17. tan(144°) * 26 = 
+
+18. tan(354°) - 83 * 51 = 
+
+19. tan(225°) * 63 = 
+
+20. sin(128°) + sin(124°) + tan(79°) = 
diff --git a/src/数学试卷/张三1/2025-09-29-15-27-37.txt b/src/数学试卷/张三1/2025-09-29-15-27-37.txt
new file mode 100644
index 0000000..38ed8ba
--- /dev/null
+++ b/src/数学试卷/张三1/2025-09-29-15-27-37.txt
@@ -0,0 +1,19 @@
+1. 16 - 55 * 15 - 100 = 
+
+2. 34 / 75 = 
+
+3. 62 + 10 = 
+
+4. 98 + 83 = 
+
+5. 96 / 92 + 41 + 67 = 
+
+6. 92 / 98 * 61 / 2 = 
+
+7. 51 - 25 / 54 + 61 = 
+
+8. 79 + 97 = 
+
+9. 28 - 27 + 96 = 
+
+10. 24 + 73 = 
diff --git a/src/数学试卷/张三1/2025-09-29-15-28-00.txt b/src/数学试卷/张三1/2025-09-29-15-28-00.txt
new file mode 100644
index 0000000..123fa64
--- /dev/null
+++ b/src/数学试卷/张三1/2025-09-29-15-28-00.txt
@@ -0,0 +1,39 @@
+1. √76 + √53 = 
+
+2. √19 / 17 + 85 = 
+
+3. 3² + 98 = 
+
+4. 100² / 6² + 2 = 
+
+5. 19² + 99 = 
+
+6. √75 + √60 = 
+
+7. √22 * 20 = 
+
+8. √42 * 22 = 
+
+9. 84² - 51² / 87 = 
+
+10. √62 * 18² + 40 = 
+
+11. √73 + 65 = 
+
+12. 55² * 75 = 
+
+13. √56 + 34² = 
+
+14. 63² + 94 / 27 = 
+
+15. 77² / √78 * 16 = 
+
+16. 14² * 55² = 
+
+17. 82² * 11 = 
+
+18. √69 * 98 = 
+
+19. √47 / 24 / 72 = 
+
+20. 54² - 84 =