1. The problem statement, all variables and given/known data Let f(x)=a(7-x^2) find in terms of a, the equations of the lines tangent to these curves at x=-1. 2. Relevant equations ? 3. The attempt at a solution So I took the derivative of f(x). f'(x)=a(-2x)+7-x^2 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 dont know where I went wrong.