1.

Prove that : Cos 20° + Cos 100° + Cos 140º = 0​

Answer»

Step-by-step EXPLANATION:

cos20∘+cos100∘+cos140∘

=(cos20∘+cos140∘)+COS(90∘+10∘)

=2cos80∘cos60∘−sin10∘=cos80∘−sin10∘

=sin10∘−sin10∘=0



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