A) \[\sin \,36{}^\circ \]
B) \[\text{cos }36{}^\circ \]
C) \[\sin \,7{}^\circ \]
D) \[\text{cos }7{}^\circ \]
Correct Answer: D
Solution :
[D]The given expression is equal to \[(\sin 47{}^\circ +\sin 61{}^\circ )-(\sin 11{}^\circ +\sin 25{}^\circ )\] |
\[=2\sin 54{}^\circ cos7{}^\circ -2sin18{}^\circ \cos 7{}^\circ \] |
\[=2\cos 7{}^\circ (\sin 54{}^\circ -\sin 18{}^\circ )\] |
\[=2\cos 7{}^\circ \left[ \frac{\sqrt{5}+1}{4}-\frac{\sqrt{5}-1}{4} \right]=\cos 7{}^\circ .\] |
You need to login to perform this action.
You will be redirected in
3 sec