Question

Como resolver? 3x - y = 9
xy = 12

Answer 1

{3x - y =9 --->3x = 9+y -->x = (9+y)/3
{xy = 12

$\frac{9+y}{3}.y=12$

$\frac{9y+y^2}{3}=12$

$y^2+9y=36 y^2+9y-36=0$
Δ= 81+144=225
√Δ=±√225=±15

y' = (-9-15)/2= -12
y"= (-9+15)/2= 3

xy = 12
            Para y = -12            Para y = 3
                     x = -1                       x = 4