SOLUTION: If (a,8) is a point on the graph y=x^2+2x, what is a?

Algebra ->  Graphs -> SOLUTION: If (a,8) is a point on the graph y=x^2+2x, what is a?      Log On


   

Question 788159: If (a,8) is a point on the graph y=x^2+2x, what is a?
Found 2 solutions by josgarithmetic, mananth:
Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
y=8 and x=a, but a is unknown.
x%5E2%2B2x=x%28x%2B2%29=8
or more useful to work with,
x%5E2%2B2x-8=0
%28x%2B4%29%28x-2%29=0

Obvious values for x are -4 or 2.
a is either -4 or positive 2.

Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
(a,8) is a point on the graph y=x^2+2x, what is a?
plug x=a and y=8
since (a,8) satisfies the equation
8=a^2+2a
a^2+2a-8=0
a^2+4a-2a-8=0
a(a+4)-2(a+4)=0
(a+4)(a-2)=0
a=-4 OR 2