Prove that
(i)
(ii)
(i)sin(50° + θ)cos(20° + θ) - cos(50° + θ)sin(20° + θ)
= sin(50° + θ - (20° + θ))(using sin(A - B) = sinAcosB - cosAsinB)
= sin(50° + θ - 20° - θ)
= sin30°
(ii)cos(70° + θ)cos(10° + θ) + sin(70° + θ)sin(10° + θ)
= cos(70° + θ - (10° + θ))(using cos(A - B) = cosAcosB + sinAsinB)
= cos(70° + θ - 10° - θ)
= cos60°