Q27 of 186 Page 345

Write the value of tan 10° tan 20° tan 70° tan 80°.

Consider tan 10° tan 20° tan 70° tan 80°

= tan 10° tan 20° tan (90° – 20°) tan (90° – 10°)


= tan 10° tan 20° cot 0° cot 10°


= tan 10° cot 10° tan 20° cot 20°


= 1 × 1


= 1


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