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Evaluate: ∫ ex sin4x - 41 - cos4x dx
Let I = ∫ ex sin4x - 41 - cos4x dx =∫ ex sin2(2x) - 41 - cos2(2x) dx = ∫ ex 2 sin2x cos2x- 42sin2(2x) dx [ Using, sin2x = 2sinx.cosx and 2sin2x = 1 - cos ( 2x ) ] = ∫ ex 2 ( sin (2x ) cos ( 2x ) - 2 )2sin2(2x) dx = ∫ ex sin (2x ) cos ( 2x )sin2(2x) - 2sin2(2x) dx = ∫ ex cot (2x ) -2cosec2(2x) dxNow, let f ( x ) = cot ( 2x ) then f ( x ) = -2cosec2 ( 2x )I = ∫ ex f ( x ) + f' ( x ) dx
So, I = ex f ( x ) + C = ex cot ( 2x ) + C, Where C is a constanttherefore, ∫ ex sin4x - 41 - cos4x dx = ex cot ( 2x ) + C
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