Differentiate the law of Cosine

ryank614
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It is a simple math question, but I am stuck.

The law of cosines is

R^2=h^2 + r^2 - 2 h r cos (theta). Theta is of course the angle facing R.

To differentiate, I first set

r^2 - 2hr cos\Theta+ (h^2-R^2) = 0

2 r \dot{}r - 2 h cos\Theta \dot{}r + (h^2-R^2) = 0.

Is there any way to put h^2-R^2 in terms of \dot{}\theta or d\theta/dt
 
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Arr, nevermind. I got it.
 
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