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Math Help - Partial Derivative

  1. #1
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    Partial Derivative

    Please help me in these 2 problems:

    1. f(x,y)= x^2 / y, need fx and fy!

    2.f(x,y)= x sin(xy), need fx and fy!
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by littlesohi View Post
    Please help me in these 2 problems:

    1. f(x,y)= x^2 / y, need fx and fy!

    2.f(x,y)= x sin(xy), need fx and fy!
    to find fx, pretend y is a constant and differentiate as usual. to find fy, pretend x is a constant and differentiate as usual. where can you get with that?
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  3. #3
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    so for the first one, I think fx = 2x but for fy I get confused can you help me please! I know the rules butusing the product or quotient rule confuses me.
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    Quote Originally Posted by littlesohi View Post
    so for the first one, I think fx = 2x but for fy I get confused can you help me please! I know the rules butusing the product or quotient rule confuses me.
    how is fx = 2x?

    if you wanted to differentiate x^2 / 3 what would that be?
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  5. #5
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    its over y! and for fx y is a constant no?
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  6. #6
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    Yes, that is true. And to differentiate x^2/y with respect to y, think of it as A/y= Ay^{-1}. What is the derivative of that?
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  7. #7
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by littlesohi View Post
    its over y! and for fx y is a constant no?
    my point is, the constant stays! if you have a constant multiplying a variable, then the constant does not disappear when you differentiate. it stays there and multiplies the variable. this is a rule of differentiation you should be familiar with. \frac d{dx} [cf(x)] = c \frac d{dx}f(x)
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