Question

(Mack-SP) Se ( x-y)² - (x+y)² = -20 , então x.y é igual a : *


-1
0
5
10
1/5

Answer 1

Resposta:

( x-y)² - (x+y)² = -20

**********a²-b²=(a-b)*(a+b)

( x-y)² - (x+y)² = [(x-y)-(x+y)]* [(x-y)+(x+y)]

( x-y)² - (x+y)² =(x-y-x-y)*(x-y+x-y)

( x-y)² - (x+y)² =(-2y)*(2x) =-4xy

( x-y)² - (x+y)² = -20

-4xy=-20

xy=5