find in terms of a, the equations of the lines tangent to these curves at x=-1.
The Attempt at a Solution
So I took the derivative of f(x).
then i plugged in -1 into f'(x)
and i got f'(-1)=2ax+7+1=2ax+8
but the answer to the problem is y=2ax+8a.
I don't know where I went wrong.