MCQ
The function $\sin x - \cos x$ is increasing in the interval
- A$\left[ {{{3\pi } \over 4},{{7\pi } \over 4}} \right]$
- ✓$\left[ {0,{{3\pi } \over 4}} \right)$
- C$\left[ {{\pi \over 4},{{3\pi } \over 4}} \right]$
- DNone of these
Now $f(x)$ is increasing function of $x$ , if
$f'(x) = \cos x + \sin x > 0$ or $\sqrt 2 \cos \left( {x - \frac{\pi }{4}} \right) > 0$
==>$0 \le x < \frac{{3\pi }}{4}i.e.\,\,\,f'(x) > 0$ in $\left[ {0,\frac{{3\pi }}{4}} \right)$.
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