Question

find the real solutions

x= y^2 - 9
x-4y-12= 0

I got x= -3 and y= 7 and x= 40

but how do i know what x to use and whats the ordered pair? I'm confused! help please!

Answer 1

I hope you used substitution and replace the x of the second equation with the x value of the first, thus...

(y^2 - 9) - 4y - 12 = 0
y^2 - 4y - 21 = 0
(y-7)(y+3) = 0
then y = 7 or y = -3

if y = 7 go back to first equation for
x = 7^2-9 = 40

if y=-3, then x = (-3)^2 - 9 = 0

so your two points are (40,7) and (0,-3)