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# Differentiation chain rule help.... Watch

1. Find dy/dx y=2cos 7x

How do you do this?
Is u=7x and y=2cos ?
And then you find du/dx = 7 and dy/dx ? :|
2. y = 2cos(7x).

Let u = 7x so y = 2cos(u).

Then dy/dx = dy/du * du/dx.
3. General chain rule is:

n x (fx)^n-1 x (f'x)

2 x 1 x (cos7x)^0 x -7sin7x

= -14sin7x
4. Cheers guys

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Updated: December 11, 2010
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