Calculation of r4 using formula given above
double r4 = ( r1 * r2 * r3 ) / ( r1 * r2 + r2 * r3 + r1 * r3 + 2.0 * sqrt ( r1 * r2 * r3 * ( r1 + r2 + r3 ) ) ) ; cout << fixed << setprecision ( 6 ) << r4 << ' ' ; return 0 ; }