A) [-1, 1]
B) \[(-\infty ,-6)\]
C) \[(6,+\infty )\]
D) \[[6,+\infty )\]
Correct Answer: D
Solution :
\[f(x)=8ax-a\sin 6x-7x-\sin 5x\] |
\[f'(x)=8a-6a\cos 6x-7-5\cos 5x=8a-7\]\[-6a\cos 6x-5\cos 5x\] |
f (x) is an increasing function |
\[f'(x)\ge 0\] |
\[\therefore \] \[8a-7\ge 6a+5\]\[\Rightarrow \]\[2a\ge 12\,\,;\,\,a\ge 6\,\,;\,\,a\in [6,\infty )\] |
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