例3.1求一元二次方程的根

 1 import java.util.Scanner;
 2 public class cjava {
 3     public static void main(String[] args) {
 4         float a,b,c,x1,x2;
 5         Scanner s=new Scanner(System.in);
 6         System.out.println("輸入a,b,c的值:");
 7         a=s.nextInt();
 8         b=s.nextInt();
 9         c=s.nextInt();
 
10         x1=(float)((-b+Math.sqrt(b*b-4*a*c))/(2*a));
11         x2=(float)((-b-Math.sqrt(b*b-4*a*c))/(2*a));
12         System.out.println("x1="+x1);
13         System.out.println("x2="+x2);
14     }
15 }

例3.2求三角形面積

 1 import java.util.Scanner;
 2 import java.lang.*;
 3 public class cjava {
 4     public
 
 static void main(String[] args) {
 5         float a,b,c,x1,x2;
 6         double s,area;
 7         Scanner g=new Scanner(System.in);
 8         System.out.println("輸入a,b,c的值:");
 9         a=g.nextInt();
10         b=g.nextInt();
11         c=g.nextInt();
12         if(a+b>c&&b+c>a&&a+c>b)
 
13         {
14         s=(a+b+c)/2;
15         area=Math.sqrt(s*(s-a)*(s-b)*(s-c));
16         System.out.println("area="+area);
17         }
18         else
19             System.out.println("it is not a trilateral!");
20     }
21 }

例3.3判斷字元大小寫，大寫轉換為小寫，小寫不轉換

 1 import java.util.Scanner;
 2 public class cjava {
 3     public static void main(String[] args) {
 4         char ch;
 5         Scanner g=new Scanner(System.in);
 6         System.out.println("輸入ch:");
 7         String s;
 8         s=g.next();
 9         ch=s.charAt(0);
10         if(ch>='A'&&ch<='Z')
11         {
12         ch+=32;
13         System.out.println(ch);
14         }
15         else
16             System.out.println(ch);
17     }
18 }

2.今天不知道怎麼用數學函式，百度查詢到java.lang

3明天繼續寫例題