Question

se xy=20 e 20 e x-y=8 qual o valor de x+y?

Answer 1

xy = 20
y = 20/x

x - y = 8
x - (20/x) = 8
( x^2 - 20 )/ x = 8
x^2 - 8x - 20 = 0

delta = 64 + 80 = 144

x1 = (8 + 12) / 2 = 10
x2 = (8 - 12) / 2 = -2

10y = 20
y = 2
10 - 2 = 8 (verdadeiro)

x + y = 10 + 2 = 12