Question

Find the derivative of f(x) = -2x2 + 11x at x = 9.
a) -25
b) -243
c) 63
d) 19

Answer 1

`\bf f(x)=-2x^2+11x\implies \left. \cfrac{df}{dx}=-4x+11 \right|_(x=9)\implies -4(9)+11\implies -25`

Answer 2

a) -25

Explanation:

First you have to find the derivative of F(x):

`f(x)=2x^(2) +11x\\Derivative=2(2x)+1(11)\\Derivative=4x+11`

Now you just have to calculate the vale of f(x) when x=9

`-4x+11=\\-4(9)+11=\\-36+11=-25`

So when x=9, the derivative of
`f(x)=2x^(2) +11x` is equal to -25