Question

Can anyone help me ? I got stuck Find the derivative of f(x) = -12x^2 + 9x at x = 6.

Answer 1

find f(x) = -12x^2+9x
find f(x+h) = -12(x+h)^2 + 9(x+h)
= -12x^2-12h^2+9x+9h

Answer 2

Now i gotta put that into this formula\[f(x+h)-f(x)\div h\]

Answer 3

so...
-12x^2-12h^2+9x+9h -(-12x^2)+9x)
-12x^2-12h^2+9x+9h +12x^2-9x combine like terms

-12h+9h/h here is where i got stuck

Answer 4

*-12h^2+9h/h

Answer 5

find f(x+h) = -12(x+h)^2 + 9(x+h)
= -12x^2-12h^2+9x+9h ********incorrect

\((a+b)^2= a^2+2ab+b^2 \)
where did your '2ab' term go ?

Answer 6

idk i didnt know there was a 2ab term

Answer 7

now you know,
so whats (x+h)^2= ... ?

Answer 8

@hartnn i solved that

Answer 9

i am glad :)