Question

Prove that cos55° + cos65° + cos175° = 0.​

Answer 1

Answer:

Refer to the attachment!!

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Answer 2

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cos55 + cos65 +cos 175 = 0 

(cos55 + cos65) + cos175 

=2 cos(120/2) cos(-10/2) + cos175 [Identity (cosA + cosB)] 

=2 cos60 cos(-5) + cos175 

=2x1/2 cos5 + cos175 [cos 60=1/2] 

=cos5 + cos(180-5) 

=cos5 - cos5 = 0