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Question: If y = \(\cos^{- 1}\left( \frac{5\cos x - 12\sin x}{13} \right)\), \(x \in \left( 0,\frac{\pi}{2} \r...

If y = cos1(5cosx12sinx13)\cos^{- 1}\left( \frac{5\cos x - 12\sin x}{13} \right), x(0,π2)x \in \left( 0,\frac{\pi}{2} \right), then dydx\frac{dy}{dx} is equal to

A

1

B

–1

C

0

D

None of these

Answer

1

Explanation

Solution

y = cos–1 (513cosx1213sinx)\left( \frac{5}{13}\cos x - \frac{12}{13}\sin x \right)

= cos–1(cosacosx – sinasinx)

= cos–1(cos(x + a)) = x + a

\ dydx\frac{dy}{dx} = 1