A) \[\cos x\]
B) \[\cos 2x\]
C) \[\cos 3x\]
D) \[\cot x\]
Correct Answer: C
Solution :
Obviously here \[\cos 3x\]is not decreasing in \[\left( 0,\frac{\pi }{2} \right)\] because \[\frac{d}{dx}\cos 3x=-3\sin 3x\] But at \[x=75{}^\circ ,\,\,-3\sin 3x>0\]. Hence the result.You need to login to perform this action.
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