Find an angle  whose rate of increase twice is twice the rate of decrease of its cosine.

Explanation

Let `x=cos theta`


Differentiating both sides with respect to `t`, we get



`frac{d x}{d t}=frac{d(cos theta)}{d t} `


`=-sin theta frac{d theta}{d t}`



But it is given that `frac{d theta}{d t}=-2 frac{d x}{d t}`



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