#include <bits/stdc++.h>   #pragma comment(linker,  /STACK:1760777216 )   using namespace std;   const double Pi = 3.14159265358979323846;   int main() {     int T;     scanf( %d , &T);     while (T--) {       double R, r, k;       scanf( %lf%lf%lf , &R, &r, &k);       double x1 = 0.5 / R, x2 = 0.5 / r, rr = fabs(x1 - x2) / 2;       double x = (x1 + x2) / 2, y = 2 * k * rr, a = x / sqrt(x * x + y * y);       double dx = rr * a, dy = rr * sqrt(1 - a * a);       double res = sqrt(x * x + y * y);       printf( %.9lf n , (1 / (res - rr) - 1 / (res + rr)) / 2);     }     return 0;   }   