Question

cos36+cos72+cos216+cos252=0

Answer 1

Hi,

Here is your answer !
______________________________

To prove :

cos36° + cos72° + cos216° +cos252° = 0

Proof:

LHS

= cos36° + cos72° + cos216° +cos252°

= cos36° + cos72° + cos(180° + 36°) + cos(180° + 72°)

= cos36° + cos72° - cos36° - cos72°

= 0

= RHS _ _ [ Proved ]

[ Since, cos(180° + A) = -cosA ]