外切圆直径=两圆半径的和+两圆心距离
圆心距离用余弦定理算
AcceptCode
#include<cstdio>
#include<iostream>
#include<cstdlib>
#include<string>
#include<cmath>
#include<algorithm>
using namespace std;
#define pi 3.141592653589793238462643383249901429
int main()
{
double l1,l2,tht;
double r1,r2,r1_r2,wide;
cin>>l1>>l2>>tht;
r1=l1/2,r2=l2/2;
tht = (tht*pi)/180;
r1_r2 = sqrt( r1*r1 + r2*r2 - 2*r1*r2*cos(tht) );
wide = r1 + r2 + r1_r2;
printf("%.10lf\n",pi*(wide/2)*(wide/2));
}
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