Question
Mathematics Question on Trigonometric Functions of Sum and Difference of Two Angles
Prove that cos 4x =1-8 sin2 x cos2 x
Answer
L.H.S.= cos 4x
= cos 2(2x)
= 1-2 sin2 2x [cos 2A =1-2 sin2 A]
=1-2(2 sin x cos x)2 [sin2A = 2sin A cosA]
= 1-8 sin2 x cos2 x
= R.H.S.