5.36（Geometry：area of a regular polygon）

问题及代码：

package first;

import java.util.Scanner;

public class MyTriangle {

public static void main(String[] args) {
System.out.println("请输入一个正多边形的边数和该正多边形的边长：");
Scanner a = new Scanner(System.in);
double s = 0;
int n = a.nextInt();
double side = a.nextDouble();
while (true) {
if (n > 0 && side > 0) {
s = area(n, side);
System.out.println("该正多边形的面积为：" +s);
break;
} else {
System.out.println("输入非法，请重新输入！");
}
}
}

public static double area(int n, double side) {
double s = 0;
double b = n * side * side;
s = (b / (4 * Math.tan((Math.PI / n))));
return s;
}
}

运行结果;