Question

resolva o sistema (U = R)

x=4y
y*-2x=9

*=ao quadrado

Answer 1

x=4y 
y²-2x=9
y² - 2 (4y) =9
y² - 8y -9 =0
Δ=b² - 4ac
Δ= (-8)² - 4.1. (-9)
Δ=64 + 36
Δ=100

y= -b +/- √Δ / 2a
y= - (-8) +/- √100 / 2.1
y'= $\frac{8+10}{2}$
y'= $\frac{18}{2}$
y'= 9
y''= $\frac{8-10}{2}$
y''= $\frac{-2}{2}$
y''= -1

Substituindo:
x= 4y
x= 4.9= 36