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Posted by on Thursday, March 1, 2012 at 11:37pm.

Given y^4 -x^4=16 find and simplify d2y/dx2 using implicit differentiation.
I got the first derivative which was x^3/y^3 and no im am stuck on using implicit differentiation for the second derivative part

  • calculus - , Friday, March 2, 2012 at 2:18pm

    y^4 - x^4 = 16
    4y^3 y' - 4x^3 = 0
    y' = x^3/y^3

    y'' = (3x^2*y^3 - x^3*3y^2*y')/y^6
    = 3x^2(y-xy')/y^4
    = 3x^2 (y-x*x^3/y^3)/y^4
    = 3x^2 (y^4 - x^4)/y^7
    = 48x^2/y^7

    or,

    y^3 y' = x^3
    3y^2 y'^2 + y^3 y'' = 3x^2
    3y^2 (x^6/y^6) + y^3 y'' = 3x^2

    y^3 y'' = 3x^2 - 3x^6/y^4
    y'' = 3x^2 (y^4 - x^4)/y^7

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