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    Need some help please.

    Any ideas of how you would differentiate ?.

    Is it y = -20 cos (pi x 19 / 12)?

    Cheers
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    Are you sure the equation came out right or is it supposed to look like something else?
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    the question is: find dy/dt and calculate the rate of change when t = 19. The original equation was: y = 10sin (pi x t / 12).
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    (Original post by Slicksomnia)
    Need some help please.

    Any ideas of how you would differentiate ?.

    Is it y = -20 cos (pi x 19 / 12)?

    Cheers
    Do you mean y=10\sin\left(\frac{19\pi}{12}x\  right)?

    If so, use:

    y = 10\sin(u) where u = \frac{19\pi}{12}x

    Then:

    \frac{dy}{dx} = \frac{dy}{du}\frac{du}{dx}



    This is the 'chain rule'.

    If you don't mean that...clarify?


    EDIT: Oh, you already did clarify. In that case:

    y = 10\sin(u) where u = \frac{\pi}{12}t

    And you can still use the chain rule to solve it.

    To find the rate of change at t = 19, remember that differentiation gives the rate of change, so you just put t=19 into your new equation.

    You cannot put t=19 straight into your first equation (like you tried to), that doesn't make any sense. You have a function for y in terms of t. To find the rate of change, you differentiate y with respect to t. This new equation is the one you must substitute t=19 into.
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    (Original post by dring)
    Do you mean y=10\sin\left(\frac{19\pi}{12}x\  right)?

    If so, use:

    y = 10\sin(u) where u = \frac{19\pi}{12}x

    Then:

    \frac{dy}{dx} = \frac{dy}{du}\frac{du}{dx}



    This is the 'chain rule'.

    If you don't mean that...clarify?


    EDIT: Oh, you already did clarify. In that case:

    y = 10\sin(u) where u = \frac{\pi}{12}t

    And you can still use the chain rule to solve it.

    To find the rate of change at t = 19, remember that differentiation gives the rate of change, so you just put t=19 into your new equation.

    You cannot put t=19 straight into your first equation (like you tried to), that doesn't make any sense. You have a function for y in terms of t. To find the rate of change, you differentiate y with respect to t. This new equation is the one you must substitute t=19 into.
    Thanks for the help. I think I worked it out correctly.
 
 
 
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