Correct Answer - Option 1 : 1
Formula used :
cos θ. cos (60° - θ). cos (60° + θ ) = (1/4) cos 3θ
sec θ = 1/cos θ
Calculations :
(cos 25°. cos 35°. cos 85°. sec 75°) × 4
⇒[cos 25°. cos(60° - 25°) . cos(60°+ 25°). sec 75°] × 4
⇒ [(1/4) cos(3 × 25°). sec 75°] × 4
⇒ (1/4) [cos 75°. sec 75°] × 4
⇒ 1
∴ Option 1 is the right answer.
