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Thread: Derivatives

  1. #1
    Junior Member Fnus's Avatar
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    Derivatives

    I'm at such a loss.
    In exercise 4 I don't even know where to being, and in exercise 9 the x=a confuses me.
    Thanks in advance
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  2. #2
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    4a) We have $\displaystyle 2x+y=6; x=1 \implies y=4$
    Also we know the gradient; $\displaystyle m=-2$
    Differentiate $\displaystyle y=x^2+ax+b$

    $\displaystyle \implies \frac {dy}{dx} = 2x+a$

    $\displaystyle \implies 2x+a=-2$

    $\displaystyle x=1; 2(-1)+a=-2$

    $\displaystyle \implies a=0$

    $\displaystyle \implies y=x^2+b$

    $\displaystyle x=1, y=-4; -4=1^2+b$

    $\displaystyle \implies b=-5$

    b is similar so ill let you try.
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