Question

Find the derivative of f(x) = -4x2 + 11x at x = 10
Could someone help me please? I understand how to go about the problem, I just can't seem to get the right answer! Thank you kindly!!

Answer 1

is it possible for you to show your steps?
It will help us to know where you are getting stuck at

Answer 2

Yes! Let me show my work, just give bare with me

Answer 3

So I am using (f(x+h)-f(x))/h.

(-4(x+h)^2+11(x+h))-(-4x^2+11x)
I distributed everything:
(-4(x^2+2xh+h^2)+11x+11h)+4x^2-11x

and this is where I get stuck, because everything after this just goes down hill. It's pretty sad.

Answer 4

instead of distributing
take -4 { (x+h)^2 - x^2} +11{(x+h)-h} /h
hope this will help

Answer 5

correction
*11 {(x+h) -x}

Answer 6

Okay let me work through and see if I did it correctly.

Answer 7

I am still stumped, Niksva.

Answer 8

[-4 { (x+h-x) (x+h+x)} +11 h ] /h
[-4{h*(2x+h) + 11h] /h
[-4 {2xh+h^2 } + 11h]/h
[-8xh -4h^2 +11h]/h
-8x -4h + 11
apply limit h tend into 0
therefore you get
-8x+11
put x = 10
to find the final solution

Answer 9

Wow, thank you very much. I see where I went wrong. This was very helpful; you rock.

Answer 10

:P