SOLUTION: if y =sqrt(cos x sqrt cos x sqrt (cos(x)* ....to ∞))), find dy/dx

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Question 1158465: if y =sqrt(cos x sqrt cos x sqrt (cos(x)* ....to ∞))),
find dy/dx
Answer by ikleyn(52781) About Me  (Show Source):
You can put this solution on YOUR website!
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if y = sqrt(cos(x) * sqrt (cos(x) * sqrt (cos(x)* ....to ∞))).

find dy/dx
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Square both sides.  You will get   

    y%5E2 = cos(x)*y.


Cancel "y" in both sides. You will get

    y = cos(x).


Take the derivative

    y' = -sin(x).


It is your answer.

Solved.