Mark the Correct alternative in the following:
cos 35o + cos 85o + cos 155o =
cos 35° + cos 85° + cos 155°
= 2 + cos 155°
= 2cos 60° cos 25° + cos (180°-25°)
= 2 ⋅ 1/2 ⋅ cos 25° - cos 25°
= cos 25° - cos 25°
= 0 (Ans)