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    There's a question which confuses me because of its wording.

    Given that u=(1+x)/(1-x) , find du/dx.

    I can do that part, but then the following wording confuses me:

    using this result, and the chain rule, show that if y=((1+x)/(1-x))^3 , dy/dx = (6(1+x)^2)/((1-x)^4).

    I can do the second part using the quotient rule. Does that answer the question?

    Thanks
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    You have to use the chain rule for the second part since it is a function within a function.

    dy/dx = du/dx x dy/du

    du/dx is your result.
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    I thought about that, but then where does dy/du come from?
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    (Original post by thegold94)
    I thought about that, but then where does dy/du come from?
    Well, (x+1)/(x-1) is u.
    So you can substitute this into the second equation they give you and you will see what I mean.
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    I think I've got it. If u= (1+x)/(1-x), then I think I take y=u^3, differentiate that to dy/du = 3u^2, stick u in there and then end up multiplying 3(1+x)^2 / (1-x)^2 to get 6(1+x)^2 / (1-x)^4. That actually works. Thanks
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    (Original post by thegold94)
    I think I've got it. If u= (1+x)/(1-x), then I think I take y=u^3, differentiate that to dy/du = 3u^2, stick u in there and then end up multiplying 3(1+x)^2 / (1-x)^2 to get 6(1+x)^2 / (1-x)^4. That actually works. Thanks
    You're welcome.
 
 
 
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