Question

Se x + y = 20 e x - y = 5 calcule (x2 - y2).

Answer 1

x² - y² = (x+y) .(x-y)

x² - y² = (20). (5)

x² - y² = 100

Answer 2

Resposta: 100

Explicação passo-a-passo:

$\left \{ {{x+y=20} \atop {x-y=5}} \right. \\\\x= 5 + y\\\\5 + y + y = 20\\\\5 + 2y = 20\\2y = 20 - 5\\2y= 15\\y = 15/2\\\\x= 5 + 15/2 = 25/2\\\\x^{2} = (25/2)^{2} = 625/4\\y^{2} = (15/2)^{2} = 225/4\\\\625/4 - 225/4 = 400/4 = 100$