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Math Help - Chain Rule Problem

  1. #1
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    Chain Rule Problem

    The question gives a reeeallly weird answer. Perhaps someone could confirm or help me out on this. It's extra practice for me.

    Let y= u^3 + 6u , where u= 2x^4 + 3x^2 - 2 Find dy/dx. Leave your answer in terms of u and x.
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  2. #2
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    Quote Originally Posted by mike_302 View Post
    The question gives a reeeallly weird answer. Perhaps someone could confirm....
    Sure! Post your steps and final answer, and we'll be glad to check it over.
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  3. #3
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    well, what I did was subbed in the quartic function for 'u' and then applied the chain rule to the first part, and I expanded the second part out, and took its derivative. Now that gets me something messy. The answer in the back gives me some silly answer that has a 'u' and an 'x' in it. (3u^2+6)(8x^3+6x)

    Makes no sense to me.
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    Quote Originally Posted by mike_302 View Post
    well, what I did was subbed in the quartic function for 'u' and then applied the chain rule to the first part, and I expanded the second part out, and took its derivative. Now that gets me something messy. The answer in the back gives me some silly answer that has a 'u' and an 'x' in it. (3u^2+6)(8x^3+6x)

    Makes no sense to me.
    It's fine.

    If you wanted to, you could replace the u's with 2x^4 + 3x^2 - 2, but it's not necessary... infact you've been told to keep it in terms of u as well as x.
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