A) \[\cos 43{}^\circ \]
B) \[\cos 7{}^\circ \]
C) \[\cos 53{}^\circ \]
D) None of these
Correct Answer: D
Solution :
\[\frac{1}{4}\{\sqrt{3}\cos {{23}^{o}}-\sin {{23}^{o}}\}\] \[=\frac{1}{2}\{\cos {{30}^{o}}\cos {{23}^{o}}-\sin {{30}^{o}}\sin {{23}^{o}}\}\] \[=\frac{1}{2}\,\cos \,({{30}^{o}}+{{23}^{o}})=\frac{1}{2}\,\cos \,{{53}^{o}}.\]
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