A) \[\left[ \frac{3\pi }{4},\frac{7\pi }{4} \right]\]
B) \[\left[ 0,\frac{3\pi }{4} \right)\]
C) \[\left[ \frac{\pi }{4},\frac{3\pi }{4} \right]\]
D) None of these
Correct Answer: B
Solution :
We have, \[f'(x)=\cos x+\sin x\] Now \[f(x)\]is increasing function of x, if \[f'(x)=\cos x+\sin x>0\]or \[\sqrt{2}\cos \left( x-\frac{\pi }{4} \right)>0\] Þ\[0\le x<\frac{3\pi }{4}i.e.\,\,\,f'(x)>0\]in \[\left[ 0,\frac{3\pi }{4} \right)\].You need to login to perform this action.
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