sum of the squares of 3 no . is 138 and the sum of their products taken two at a time is 131 . find the sum ?
"( a + b + c ) 2 = a 2 + b 2 + c 2 + 2 ( ab + bc + ca ) = 138 + 2 * 131 a + b + c = √ 400 = 20 a"
sqrt(add(138, multiply(131, const_2)))