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
