SOLUTION: y=(x-3)(-x-4) y=x^2-16

Question 551022: y=(x-3)(-x-4)
y=x^2-16
Answer by ankor@dixie-net.com(22740) (Show Source): You can put this solution on YOUR website!
y=(x-3)(-x-4)
y=x^2-16
Write y = y, and solve for x
x^2 - 16 = (x-3)(-x-4)
FOIL
x^2 - 16 = -x^2 - 4x + 3x + 12
x^2 - 16 = -x^2 - x + 12
Combine like terms on the left
x^2 + x^2 + x - 12 - 16 = 0
2x^2 + x - 28 = 0
Factors to
(2x-7)(x+4) = 0
two solutions
2x = 7
x = 3.5
and
x = -4
:
Check this using x=-4
y = x^2 - 16
y = (-4)^2 - 16
y = 16 - 16
y = 0
and
y = (-4-3)(-(-4)-4)
y = -7*(4-4)
y = 0
:
You can check x=3.5
:
Graph the two original equations, you can they intersect when x=-4 and x=3.5

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