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Stationary Point after Partial Differentiation

  1. Jan 17, 2012 #1
    1. The problem statement, all variables and given/known data
    A question in a book has partially differentiated a function

    f(x,y) = x^2 + 8xy^2 + 2y^2

    df/dx = 2x + 8y^2 = 0 at stationary point (eqn 1)
    df/dy = 16xy + 4y = 0 at stationary point (eqn 2)


    2. Relevant equations



    3. The attempt at a solution

    It then states;

    From (eqn 2) either
    y = 0, or 16x + 4 = 0
    y = 0, or x = -1/4

    I can understand how y=0, but how do they conclude that 16x + 4 = 0

    Thank you
     
  2. jcsd
  3. Jan 17, 2012 #2
    I've realised they've just factored out the y!
     
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