Cos2a+sin^2a; sin40/2cos20;sin100/2cos50
Cos 2a + sinˇ2 a = cosˇ2a -sinˇ2a + sinˇ2a = cosˇ2a sin40/2cos20 = 2.sin20.cos20/2.cos20 = sin20 sin100/2.cos50 = sin (2.50)/2.cos50 = 2.sin50.cos50/2.cos50 = sin50