Question

Sabendo-se que (x+y)²= 18 e x²+y² = 10 o valor de xy é?

Answer 1

(x + y)^2 = x^2 + 2xy + y^2 = 18

x^2 + y^2 + 2xy = 18

10 + 2xy = 18

2xy = 18 - 10

2xy = 8

xy = 8/2

xy = 4 ←←

Answer 2

(x + y)² = x² + 2xy + y² = 18
x² + y² = 10
2xy + 10 = 18
2xy = 8
xy = 8/2
xy = 4