UVA 10522 Height to Area（知三角形三高求面积）

思路：海伦公式，

AC代码：

 #include<bits/stdc++.h>
 using namespace std;
 int main()
 {
     int n;
     scanf("%d",&n);
     double ha, hb, hc, a, b, c;
     while(~scanf("%lf %lf %lf",&ha,&hb,&hc))
     {
         a = 2.0 / ha;
         b = 2.0 / hb ;
         c = 2.0 / hc;
         if(a <= 0.0 || b <= 0.0 || c <= 0.0 || a >= b+c || b >= a+c || c >= a+b )
         {
             printf("These are invalid inputs!\n");
         }
         else {
             double p = (a + b + c)*0.5;
             double s = p * (p - a)*(p - b)*(p - c);
             printf("%.3f\n",sqrt(1.0 / s));
         }
     }
     return ;
 }