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U substitution for differentiation?

  1. Aug 5, 2004 #1
    How do I evaluate:

    d/dt sqrt [ t^4 + t^2 ]= 0
    to get a max/min value.

    can I make a u substitution of some sort?
  2. jcsd
  3. Aug 5, 2004 #2


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    Staff Emeritus
    Science Advisor

    Yes, that's basically just the "chain rule".

    Let u= t4+ t2

    then d sqrt(t4+ t2)/dt= d u1/2/du* du/dt
    = (1/2)u-1/2 * (4t3+ 2t)
    = (1/2)(t4+t2)-1/2)*(4t3+ 2t)
  4. Aug 5, 2004 #3
    Thanks for your help.
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