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anonymous

  • 5 years ago

What is the second derivative of (x^2 +5)^4? I've got the answer, but I don't know how to simplify it.... But my answer may be wrong. I got [8x(x^2 +5)^3] + [ 8(x^2 +5)^4]

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  1. anonymous
    • 5 years ago
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    nah, after the first derivative it looks like your product rule went awry

  2. anonymous
    • 5 years ago
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    what did you get for the first derivative? 8x(x^2+5)^3???

  3. anonymous
    • 5 years ago
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    I'm not surprised... I'm awful at math. :/ I got 8x(x^2 +5) +8

  4. anonymous
    • 5 years ago
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    Oops, make that 8x(x^2 +5)^3 +8

  5. anonymous
    • 5 years ago
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    whoops, wrong thread...

  6. anonymous
    • 5 years ago
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    umm, nah everybody struggles with calculus the first go round!

  7. anonymous
    • 5 years ago
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    ok, for the first derivative, don't add 8 since it is not a product rule. other than that it looks fine

  8. anonymous
    • 5 years ago
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    so y'=8x(x^2+5)^3 now to find y'' take derivative of this and use product rule with the first product being 8x and then the second term of the product being (x^2+5)^3

  9. anonymous
    • 5 years ago
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    I got [8x * 8x(x^2+5)^3] + [8(x^2+5)^4]

  10. anonymous
    • 5 years ago
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    But I have to simplify that (assuming that what I have is right, but it's probably not), which is what I can't figure out. I know that the GCF is 8(x^2+5)^3, and I know that the second half of the equations will be (x^2+5), but the first half is what I don't understand.

  11. anonymous
    • 5 years ago
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    derivative of 8x is just 8, so the first term will be 8*(x^2+5)^3 the next term, now instead of differentiating with respect to 8x, you do (x^2+5)^3

  12. anonymous
    • 5 years ago
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    which should give you 8x*[6x(x^2+5)^2] or 48x^2(x^2+5)^2

  13. anonymous
    • 5 years ago
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    the whole second derivative then will be those two terms added together 8*(x^2+5)^3 +48x^2(x^2+5)^2

  14. anonymous
    • 5 years ago
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    But that's not the simplified version, right?

  15. anonymous
    • 5 years ago
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    yeah, take out the GCF of 8(x^2+5)^2*[x^2+5+6x^2) and then combine like terms

  16. anonymous
    • 5 years ago
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    final answer should be something like y''= 8(x^2+5)^2*(7x^2+5)

  17. anonymous
    • 5 years ago
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    I typed that into my assignment, and it says that should be this 8(x^2+5)^3*(7x^2+5)

  18. anonymous
    • 5 years ago
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    hmm, let me double-check, but I don't think so, since the power that is common should have dropped down to 2, not 3

  19. anonymous
    • 5 years ago
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    hmm, I got the same answer when I re-did it...I don't know why it is a power of 3 to be honest

  20. anonymous
    • 5 years ago
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    I don't, either! :p Thanks for helping me, though! I really appreciate it! :)

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