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Math Help - Elasticity (Quotient) Derivative

  1. #1
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    Elasticity (Quotient) Derivative

    Hey math'ers...

    I'm trying to figure this out, it should be simple, but...

    El x f(x) = x/f(x) * f ' (x), so...

    El x f(x)/g(x) = x (f/g) * d/dx (f / g), which means...

    El x f/g = x (f/g) * (f * g ' - f ' * g), so I know the result is supposed to be... El x (f/g) = El x f - El x g, but - how do I get on?

    Any help is appreciated...

    Simon DK
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  2. #2
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    Quote Originally Posted by sh01by View Post
    Hey math'ers...

    I'm trying to figure this out, it should be simple, but...

    El x f(x) = x/f(x) * f ' (x), so...

    El x f(x)/g(x) = x (f/g) * d/dx (f / g), which means...

    El x f/g = x (f/g) * (f * g ' - f ' * g), so I know the result is supposed to be... El x (f/g) = El x f - El x g, but - how do I get on?

    Any help is appreciated...

    Simon DK
    El x f/g = x (f/g) * (f * g ' - f ' * g)

    has two errors. First, divide by f/g since the basic formula divides by f. Then use the quotient rule for d/dx(f/g), not the product rule. The result does follow simply from there.
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