The Question asks:

"Which of the following is an equation of the line tangent to the graph of

$\displaystyle f(x)= x^4 + 2x^2$ at the point where $\displaystyle f'(x)=1$? "

I found the derivative/slope to be:

$\displaystyle f'(x)= 4x^3 + 4x$

And since f'(x) = 1, I set it equal to one.

$\displaystyle 1=4x^3 + 4x$

Even if I was able to factor that out (which I can't figure out how) I don't know how to find the equation of the tangent line without a point to work from.