Question

If cos 65 degree +cos 55 degree = cos θ, find θ in radians

Answer 1

We have to find t(theta) in radians.
cos t = cos 65° + cos 55°  
We know that:
cos x + cos y = 2 · cos (x+y)/2 · cos (x - y)/2
cos t = 2 · cos (65°+55°)/2 · cos (65°-55°)/2
cos t = 2 · cos 60°· cos 5°
cos t = 2 · 1/2 · cos 5°
cos t = cos 5°
t = 5° = π/36 radians