Calculation of r4 using formula given above
let r4 = ( r1 * r2 * r3 ) / ( r1 * r2 + r2 * r3 + r1 * r3 + 2.0 * Math . sqrt ( r1 * r2 * r3 * ( r1 + r2 + r3 ) ) ) ; document . write ( r4 . toFixed ( 6 ) + " " ) ;