sin4a - cos4a = 2sin2a-1 = 1 - 2 cos2a
L.H.S. sin4 a-cos4a
- (sin2a)2 -(cos2a)2
- (sin2a-cos2a)(sin2a+cos2a)
- (sin2a-1+sin2a) 1
- (2sin2a-1) therfore, R.H.S. proved
- now, (2sin2a-1)
- 2(1-cos2a)-1
- 2-2cos2a-1
- 1-2cos2a
- proved
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