Compute f a algebraically for the given value of a fx 2x2x

Compute f \'(a) algebraically for the given value of a.

f(x) = 2x^2+x; a=-9

f \'(a)=______________

***the answer I got was -36...please let me know if that is correct!!

Solution

f(x) = 2x^2+x

f\'(x) = 4x+1

f\'(a) = 4a+1

given a = -9

f\'(-9) = 4(-9)+1

f\'(-9) = -35