Prove That ??? Cos306°+Cos234°+cos162°+Cos18° = 0

2 Answers
May 16, 2018

see below

Explanation:

cos306" is in Q.IV ":. cos306=+cos(360-306)=cos54

cos234" is in Q.III":.cos234=-cos(234-180)=-cos54

cos162" is in Q>II":.cos162=-cos(180-162)=-cos18

cos306+cos234+cos162+cos18

=cos54-cos54-cos18+cos18=0

May 16, 2018

Please see the explanation below

Explanation:

Let's transform the angles

according to the trigonometric circle
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cos(306)=cos(360-306)=cos54

cos(234)=-cos(234-180)=-cos54

cos162=-cos(180-162)=-cos18

Therefore,

cos306+cos234+cos162+cos18

=cos54-cos54-cos18+cos18

=0