A) \[\sqrt{6}\sin A\]
B) \[-\sqrt{7}\sin A\]
C) \[\sqrt{6}\cos A\]
D) \[\sqrt{7}\cos A\]
E) \[\sqrt{42}\cos A\]
Correct Answer: B
Solution :
Given, \[\sin A-\sqrt{6}\cos A=\sqrt{7}\cos A\] Replacing A by\[90{}^\circ +A,\]we get \[\sin (90{}^\circ +A)-\sqrt{6}\cos (90{}^\circ +A)\] \[=\sqrt{7}\cos (90{}^\circ +A)\] \[\Rightarrow \] \[\cos A+\sqrt{6}\sin A=-\sqrt{7}\sin A\]
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