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Homework Help: Differentiate (4sinx)(cosy)=1

  1. Oct 8, 2009 #1
    . differentiate (4sinx)(cosy)=1 w.r.t x and fine dy/dx

    Im stuck here

    (4cos x)(cos y)+ (4sin x)(-sin dy/dx[y])
  2. jcsd
  3. Oct 8, 2009 #2
    Re: differentiate

    Differentiating (4sinx)(cosy)=1 w.r.t. x:

    4cos(x)cos(y)-4sin(x)sin(y)*dy/dx = 0 since the derivative of 1 is a constant.

    is what you'll get, not whatever you wrote. you differentiate the whole function first, then multiply it with the derivative of the function inside.

    Now, just solve for dy/dx.
  4. Oct 8, 2009 #3
    Re: differentiate

    why its -4sin(x)sin(y)*dy....
    Whts its negative 4 not PLUS!
  5. Oct 8, 2009 #4
    Re: differentiate

    When you differentiate cos y, you get -siny. I just brought the negative sign out.
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