- #1
coookiemonste
- 24
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Homework Statement
Let f(x)=a(7-x^2)
find in terms of a, the equations of the lines tangent to these curves at x=-1.
Homework Equations
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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 don't know where I went wrong.