Question

if (x - y) = 10 and (x²+y²) = 18 find xy

Answer 1

use

$(x + y) {}^{2} = x {}^{2} + {y}^{2} + 2xy$

Answer 2

(x-y)= x^2+y^2-2xy ,

10= 18 -2xy ,

2xy= 18-10 ,

2xy=8

xy= 8/2

Ans xy=4