Question

Prove that
sec^2(20°)+sec^2(40°)+sec^2(80°)=36​

Answer 1

Answer:

Prove that: sec220∘+sec240∘+sec280∘=36

My Attempt:

L.H.S=sec220∘+sec240∘+sec280∘

=1cos220°+1cos240°+1cos280°

=cos240°.cos280°+cos220°.cos280°+cos220°.cos240°cos220°.cos240°.cos280°

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