数学 ACdream 1196 KIDx's Triangle

题目传送门

/*
    这道题花了好长时间AC，思路有，但是表达式少写了括号一直乱码,囧!
    注意：a==0时要特判:)
*/
#include <cstdio>
#include <algorithm>
#include <iostream>
#include <cstring>
#include <string>
#include <cmath>
using namespace std;

const int MAXN = 1e4 + 10;
const int INF = 0x3f3f3f3f;
const double PI = acos (-1.0);

double f(double k)
{
    return 1.0 * k * PI / 180;
}

int main(void)        //ACdream 1196 KIDx's Triangle
{
    //freopen ("H.in", "r", stdin);

    double a, b, c, d;
    double ae, cd, ce, de, ab, ad, be, bd;
    double x;
    while (scanf ("%lf%lf%lf%lf", &a, &b, &c, &d) == 4)
    {
        if (a == 0)
        {
            puts ("0.00");    continue;
        }

        ad = sin (f(c)) / sin (f(a+b+c));
        ae = sin (f(c+d)) / sin (f(b+c+d));
        be = sin (f(b)) / sin (f(b+c+d));
        bd = sin (f(a+b)) / sin (f(a+b+c));
        de = sqrt (be*be + bd*bd - 2 * be * bd * cos (f(d)));

        x = acos ((de*de+ae*ae-ad*ad) / (2.0 * de * ae)) * 180 / PI;

        if (x < 0)    printf ("%.2f
", 180.0 - x);
        else    printf ("%.2f
", x);
    }

    return 0;
}