要求定義和調用函數：double computeArea(doublea, double b, double c, double d, double alpha)，該函數返回任意四邊形的面積。

#include <stdio.h>
#include <math.h>
#define PI 3.14159
double computeArea(double a, double b, double c, double d, double alpha);
int main(void)
{
double a, b, c, d, alpha;
scanf("%lf%lf%lf%lf%lf", &a, &b, &c, &d, &alpha);
alpha = alpha * PI / 360;
printf("%f\n", computeArea(a, b, c, d, alpha));
return 0;
}
double computeArea(double a, double b, double c, double d, double alpha)
{
double s,S;
s=(a+b+c+d)/2;
S=sqrt((s-a)(s-b)(s-c)(s-d) - abcd*cos(alpha)*cos(alpha));
return S;
}