Question

Prove that cos10+cos 110+cos130 =0

Answer 1

hello...
cos 10 + cos 110 + cos 130 = (cos 10 + cos 110) + cos 130

= 2 cos (110 + 10)/2 * cos (110 - 10)/2 + cos 130 {using cos C + cos D = 2 cos (C + D)/2 * cos (C - D)/2 }

= 2 cos 120/2 * cos 100/2 + cos (180 - 50) ( As 130 = 180 - 50)

= 2 cos 60 * cos 50 - cos 50 (Using cos (180 - A) = - cos A)

= 2 * 1/2 * cos 50 - cos 50 ( As cos 60 = 1/2)

= cos 50 - cos 50 = 0

I hope it help you....
please mark it as a brainieist answer....

Answer 2

Step-by-step explanation:

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