See a very clear solution here: https://socratic.org/questions/582476bab72cff56d798b941#:~:text=1%20Answer&text=By%20the%20sum%20and%20difference,B%E2%88%92sinAsinB%20.&text=Use%20the%20identity%20sin2,%3D1%E2%88%92cos2%CE%B8%20.&text=This%20identity%20has%20been%20proved!
+1124 
