A) \[\frac{1}{\sqrt{2}}\]
B) \[\frac{1}{2}\]
C) \[-\frac{1}{\sqrt{2}}\]
D) 0
Correct Answer: A
Solution :
\[\cos {{15}^{o}}-\sin {{15}^{o}}=\sqrt{2}\,.\cos \,({{45}^{o}}+{{15}^{o}})=\sqrt{2}\,.\,\cos \,\,{{60}^{o}}\] \[=\sqrt{2}\,.\frac{1}{2}=\frac{1}{\sqrt{2}}\].
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