Math, asked by easymylavaram, 6 months ago

179. Prove that cos12° + cos84° + cos132°+cos156=_1/2

Answers

Answered by Anonymous

20

Step-by-step explanation:

=cos 12°+cos84°+cos132°+cos156°

=(cos12°+cos132°)+(cos84°+cos156°)

=2cos 72°cos60+2cos 120°cos36°

=cos72°-cos36°=sin18°-cos36°

=(root5-1/4)-(root5+1/4)

= -1/2

Answered by sagarrajeshwari53

0

Step-by-step explanation:

= ( cos 12 degree + cos 132 degree) + ( cos 84 degree + cos 150degree)

= cos 72 degree - cos 36 degree

= sin18 degree - cos 30 degree

= -1/2

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