Question

no sistema no 2 grau -x+y=3 xy=18

Answer 1

y=3+x

xy=18
x=18/y
x=18 / (3+x)
3x+x^2=18
x^2+3x-18=0
baskara:
$x = \frac{-b+- \sqrt{b^2-4.a.c}}{2.a} \\ x = \frac{-3+- \sqrt{3^2-4.1.(-18)}}{2.1} \\x = \frac{-3+- \sqrt{3^2-4.1.(-18)}}{2.1} = \\x= \frac{-3+- \sqrt{81}}{2} \left \{ {x' = \\ \frac{-3+9}{2} = \frac{6}{2} = 3 } \atop { x'' = \frac{-3-9}{2} = \frac{-12}{2} = -6 }} \right.$

y=3+(3)
y=6

ou

y=3+(-6)
y= -3

Portanto, x=3 e y=6  ou x=(-6) e y=-3