Question

tan20°tan30°tan40°tan80°=1
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Answer 1

Answer:

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Answer 2

Answer:

1

Step-by-step explanation:

Take L.H.S

tan 20° tan 40° tan 30° tan 80°

Multiplying & Dividing by 2:

{∵ 2 sin A sin B = cos (A – B) – cos (A + B) &

2 cos A cos B = cos (A + B) + cos (A – B)}

{∵ cos (-A) = cos A}

{∵ 2 cos A sin B = sin (A + B) – sin (A – B) &

2 cos A cos B = cos (A + B) + cos (A – B)}

{∵ sin (-A) = - sin A}

{∵ sin (180° - A) = sin A & cos (180° - A) = - cos

= 1

= R.H.S

Hence Proved