Question 892775
Not sure what you want.
{{{y<>Y}}}.


If you mean, y=8, then you have {{{8-f(x)=2x^2}}}.  This allows to have {{{f(x)=2x^2-8}}}.  If you mean, x=8 then you have {{{y-f(8)=2(8)^2}}} and then this give you {{{y=f(8)+128}}} and you do not yet know f(x) nor f(8).



STUDENT RESTATED PROBLEM:
{{{highlight_green(y=f(x)=2x^2)}}},  {{{highlight_green(y=8)}}}.
Much clearer.
f(x) is clearly defined.


{{{f(8)=2*(8)^2}}}
{{{f(8)=2*64}}}
{{{highlight(f(8)=128)}}}