Question

Can someone explain this?
Find the derivative of f(x) = 12x^2 + 8x at x = 9.

Answer 1

the formula for the derivative of an algebraic function like f(x) = a x^n is

f'(x) = an x^(n-1)

Answer 2

so for example

f(x) = 4x^3

f'(x) = 12 x^(3-1) = 12 x^2

Answer 3

so find the derivative of 12x^2 and 8x then replace x by 9 to find f'(2)

Answer 4

* f'(9)

Answer 5

the derivative gives the slope of the tangent to the curve at x = 9

Answer 6

so I have
f(x) = 12x^2 + 8x at x = 9.
and you say that
a = 12
n = 2
so 24x^1?

Answer 7

and what about the +8x

Answer 8

@welshfella

Answer 9

You must get the derivative of 8x aswell and add it to the other part of the derivative :)