Adam C.

asked • 09/13/20

Calculus chain rule and trigonometric functions

Calculus Question:


In the following equation, a and b are constants, and E is a function of the variable 􏰌t. Find expressions for 􏰍􏰎dx/dt in terms of a, b, E and dE/dt.


x = a cos E



Adam C.

I have a solution of: a sin E dE/dt, but shouldn’t the solution be: -a sin E dE/dt?
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09/13/20

1 Expert Answer

By:

Shaun L. answered • 09/13/20

Tutor
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Physics and Applied Math Student at Yale University

Adam C.

Thanks Shaun, would you mind putting the steps in, just so it is clear I’m my mind, as a previous answer I saw was asinE*dE/dt. Thanks in advance.
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09/14/20

Shaun L.

Sure, no problem. From left to right, we'll take the derivative of the equation with respect to t. Differentiating x, we get simply dx/dt. On the other side of the equation, a is a constant and gets pulled out to the front of everything else. The derivative of d/dt(cos y) is - sin y. In this case, the "y" is our E, which is also a function of t. So, applying the chain rule, we take the derivative of cos E as -sin E multiplied by the derivative of E with respect to t. So our final answer is dx/dt = - a sin E * dE/dt.
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09/14/20

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