A) \[-1\]
B) 0
C) 1
D) 2
Correct Answer: C
Solution :
\[\cot 15{}^\circ \,\,\cot 20{}^\circ \,\,\cot 70{}^\circ \,\,\cot 75{}^\circ \] \[=\tan \,\,(90{}^\circ -15{}^\circ )\tan \,\,(90{}^\circ -20{}^\circ )\,\,\cot 70{}^\circ \,\,\cot 75{}^\circ \] \[=\tan 75{}^\circ \,\,\tan 70{}^\circ \frac{1}{\tan 70{}^\circ }\cdot \frac{1}{\tan 75{}^\circ }=1\]
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