cos² 2x–cos² 6x = sin4x sin8x
Answers
Answered by
3
using Identity a sq.- b sq. we get (cos2x +cos6x) (cos2x- cos6x) and at last we will use 2sinx.cosx Identity
Answered by
10
Answer :
cos²2X - cos²6X = sin4X sin8X
L.H.S.=> cos²2X - cos²6X
[ cos²X - cos²Y = -sin(X+Y) sin(X-Y) ]
=> -sin(2X+6X) sin(2X-6X)
=> -sin(8X) sin(-4X)
=> -sin8X (-sin4X) [ sin(-X) = -sinX ]
=> sin8X sin4X
or, sin4X sin8X = R.H.S.
__Proved__
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