Posted by **Dee** on Monday, February 26, 2007 at 10:52am.

Derivative

Differentiate

f(x)=(5x-4)^2

There are two ways to do this:

(1) let u = 5x-4, and use the "chain rule", df/dx = df/du * du/dx

OR

(2) expand the polynomial to

f(x) = 25 x^2 -40x + 16

and differentialte it term-by-term.

You will get the same answer either way.

Let's use the first way, because it is something you may need for other problems

u = 5x-4

du/dx = 5

f(u) = u^2

df/dx = df/du * du/dx

= 2 u * 5 = 10(5x -4) = 50x - 40

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