Calculus - how to use the chain rule for this question
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Calculus - how to use the chain rule for this question

[From: ] [author: ] [Date: 12-05-03] [Hit: ]
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Use the chain rule to find dy/dx in terms of x if:
y = 5u^2+2u+8, u = 3x-4

The answer is 6(15x-19)
I need help with the working out. The question was set out as above and I don't understand what I have to do.

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dy/dx = dy/du * du/dx
dy/dx = (10u + 2) * 3
dy/dx = 30u + 6
dy/dx = 30(3x - 4) + 6
dy/dx = 90x - 114
dy/dx = 6(15x - 19)

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You are welcome.

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The chain rule says that if we have a function y=y(u), where u=u(x), then
dy/dx = dy/du du/dx

dy/dx = 5*2*u*du/dx + 2*du/dx = 10*(3x-4)*3 +2*3 = 30(3x-4)+6 = 90x - 114 = 6(15x- 19)
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