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Question
Evaluate the following: cot20° cot40° cot45° cot50° cot70°
Solution
cot20° cot40° cot45° cot50° cot70°
= cot(90° - 70°) x cot(90° - 50°) x 1 x cot50° x cot70°
= tan70° x tan50° x cot50° x cot70°
= tan70° x cot70° x tan50° x cot50°
= `tan70° xx (1)/(tan70°) xx tan50° xx (1)/(tan50°)`
= 1.
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