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Math Help - differention using quotient rule

  1. #1
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    differention using quotient rule

    Can anyone please help me explain why 1. is wrong?


    y = (2x^2 + bx +c) / (x^2 + -5x+4)

    1. dy/dx = (4x +b)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) (THIS IS INCORRECT)

    2. dy/dx = (4xb)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) ( this is correct)
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  2. #2
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    Hello,

    Quote Originally Posted by Goodguy View Post
    Can anyone please help me explain why 1. is wrong?


    y = (2x^2 + bx +c) / (x^2 + -5x+4)

    1. dy/dx = (4x +b)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) (THIS IS INCORRECT)

    2. dy/dx = (4xb)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) ( this is correct)
    The quotient rule says :

    \left(\frac uv\right)'=\frac{u'v-uv'}{\color{red}\bf{v^2}}

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  3. #3
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    Thanks for reply. Yeah I knew the quotient rule. But I just wanted to calculate stationary points so that dy/dx = 0 . so denominator v^2 does not matter. Its the numerator which I am concerned about. I should have pointed this out earlier. Can you tell me numerator in 1. is INCORRECT


    y = (2x^2 + bx +c) / (x^2 + -5x+4)

    1. dy/dx = (4x +b)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) (THIS IS INCORRECT)

    2. dy/dx = (4xb)(x^2 + - 5x + 4) -(2x - 5)(2x^2 + bx + c) ( this is correct)
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