Convex hdu5979

We have a special convex that all points have the same distance to origin point.
As you know we can get N segments after linking the origin point and the points on the convex. We can also get N angles between each pair of the neighbor segments.
Now give you the data about the angle, please calculate the area of the convex

Input

There are multiple test cases.
The first line contains two integer N and D indicating the number of the points and their distance to origin. (3 <= N <= 10, 1 <= D <= 10)
The next lines contain N integers indicating the angles. The sum of the N numbers is always 360.

Output

For each test case output one float numbers indicating the area of the convex. The printed values should have 3 digits after the decimal point.

Sample Input

4 190 90 90 906 160 60 60 60 60 60

Sample Output

2.000
2.598
简单题，求多边形的面积，只需要求各个三角形的面积和就可以了
ac代码：
#include <iostream>#include <cstdio>#include <cstring>#include <cmath>using namespace std;int main(){    int t,x,y;    while(cin>>x>>t)    {        double sum=0;       for(int i=0;i<x;i++)       {           scanf("%d",&y);           sum+=(t*t*sin(y/180.0*3.1415926)/2);       }       printf("%.3lf\n",sum);    }    return 0;}