Question

MACK-SP) Se (x-y)2 - (x+y)2= -20 ,entao x.y è igual a
a) 0.
b) -1.
c) 5.
d) 10.

Answer 1

(x-y)²-(x+y)²

x²-2xy+y²-(x²+2xy+y²)= -20

x²-2xy+y²-x²-2xy-y²= -20

-2xy-2xy= -20

-4xy= -20

  xy= -20/-4

  x.y= 5

Resposta → C) 5

Answer 2

Oie, Td Bom?!

■ Resposta: Opção C.

$(x - y) {}^{2} - (x + y) {}^{2} = - 20$

$(x - y - (x + y)) \: . \: (x - y + x + y) = - 20$

$(x - y - x - y) \: . \: 2x = - 20$

$( - 2y) \: . \: 2x = - 20$

$- 2y \: . \: 2x = - 20$

$- 4xy = - 20$

$xy = \frac{ - 20}{ - 4}$

$xy = \frac{20}{4}$

$xy = 5$

Att. Makaveli1996