Question

cos24°+cos55°+cos125°+cos204°=

Answer 1

⇒cos 24° +cos 55° +cos (180°-55°) +cos(180°+24°)

=cos 24° +cos 55° - cos 55° -cos 24°

=0

Answer 2

I think the correct question is this:

The value of following is cos24° + cos55° + cos 125° + cos 204° + cos300°  

A) -1/2

B) 1/2

C) 2

D) 1

Answer:

The value of  

cos24∘+cos55∘+cos125∘+cos204∘+cos300∘

We know that, cos(180∘±θ)

=−cosθ

⇒cos24∘+cos55∘+cos(18∘−55∘)

+cos(180∘+24∘)+cos(360∘−60∘)

⇒cos24∘+cos55∘−cos55∘−cos24∘+cos60∘

=cos60∘

=12

If there is any confusion please leave a comment below.