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Question
Write the value of tan10° tan 20° tan 70° tan 80° .
Solution
𝑡𝑎𝑛10° 𝑡𝑎𝑛20° 𝑡𝑎𝑛70° 𝑡𝑎𝑛80°
= cot(90° − 10° ) cot(90° − 20° ) 𝑡𝑎𝑛70° 𝑡𝑎𝑛80°
= 𝑐𝑜𝑡80° 𝑐𝑜𝑡70° 𝑡𝑎𝑛70° 𝑡𝑎𝑛80°
=`1/ (tan 80°) xx1/ (tan 70° ) xx tan 70° xx tan 80° `
= 1
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