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    How do I differentiate cos(piy)?

    Should I use chain rule??
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    The differential of any cos(f(x)) is -f'(x)sin(f(x))

    Eg d(cos(2x))/dx = -2sin(2x)
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    (Original post by Cerdic)
    The differential of any cos(f(x)) is -f'(x)sin(f(x))

    Eg d(cos(2x))/dx = -2sin(2x)
    So it's just -pisin(y)?

    No dy/dx or anything?
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    (Original post by Dinasaurus)
    So it's just -picos(y)?

    No dy/dx or anything?
    You haven't said what you're differentiating with respect to, but assuming it's y, then the answer would be -\pi sin(\pi y)
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    (Original post by Dinasaurus)
    So it's just -pisin(y)?

    No dy/dx or anything?
     \displaystyle \frac{d}{dx} \left [ \cos(\pi y) \right ] = -\pi \sin(\pi y)\frac{dy}{dx} .
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    (Original post by B_9710)
     \displaystyle \frac{d}{dx} \left [ \cos(\pi y) \right ] = -\pi \sin(\pi y)\frac{dy}{dx} .
    Or that if you're differentiating wrt x
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    (Original post by B_9710)
     \displaystyle \frac{d}{dx} \left [ \cos(\pi y) \right ] = -\pi \sin(\pi y)\frac{dy}{dx} .
    Where does that dy/dx come from? What method would be used to do this or is this just something I am expected to know?
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    (Original post by Dinasaurus)
    Where does that dy/dx come from? What method would be used to do this or is this just something I am expected to know?
    Well  \displaystyle \frac{d}{dx} \left [\cos(\pi y) \right ]= \frac{dy}{dx} \frac{d}{dy} \left [ \cos(\pi y) \right ]
    See how the dy on the top and bottom kind of cancel out leaving just d/dx (cosπy). That's what you do. Differentiate the function with respect to y then multiply by dy/dx.
 
 
 
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Updated: March 13, 2016

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