Question 788159
y=8 and x=a, but a is unknown.

{{{x^2+2x=x(x+2)=8}}}
or more useful to work with,
{{{x^2+2x-8=0}}}
{{{(x+4)(x-2)=0}}}


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