Question

Buktikan.
cos x - cos 3x + cos 5x + cos 7x = -4 cos 4x sin 2x sin x

Answer 1

Answer:

Here, L.H.S= cos x - cos 3x + cos 5x + cos 7x

= 2 sin2x sin x -2 sin 6x sin x=

= 2 sinx (sin2x - sin6x)

= 2 sinx ( - 2 sin2x . cos4x)

= - 4 sinx . sin 2x. cos4x =R.H.S

Hence proved. ..

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