hi everyone im having a really difficult time with this problem so ur help would be greatly appreciated! :)
How would you integrate sin^2cos^2?
thanks in advance
Seven answers:
anonymous
2011-03-14 00:14:32 UTC
K = ∫ sin² x cos² x dx
K = ∫ (1 - cos² x) cos² x dx
K = ∫ cos² x dx - ∫ cos⁴ x dx
K = ∫ (½ + ½ cos 2x) dx - ∫ (½ + ½ cos 2x)² dx
K = ½ x + ¼ sin 2x - ∫ (¼ + ½ cos 2x + ¼ cos² 2x) dx
K = ½ x + ¼ sin 2x - ∫ (¼ + ½ cos 2x + ¼ (½ + ½ cos 4x)) dx
K = ½ x + ¼ sin 2x - ∫ (¼ + ½ cos 2x + ⅛ + ⅛ cos 4x) dx
K = ½ x + ¼ sin 2x - ¼ x - ¼ sin 2x - ⅛ x - (1/32) sin 4x + C
K = ⅛ x - (1/32) sin 4x + C
Pure Pure
2011-03-14 00:27:52 UTC
I dont think it is 1. this is what u can do
sin^2cos^2 = (sin(2x)^2)/4
so integration of (1/4)(sin(2x)^2)
then use the u substitution 2x
u = 2x
du = 2 dx
substitute u get
(1/8)(sin(u)^2) du then evaluate integration of (sin u)^2 then times (1/8) later. u should be able to evaualte sin(u)^2 easily i believe. after that, dont forget to substitute back the value from u to x to get the correct answer. (u = 2x)
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Hemant
2011-03-14 00:15:53 UTC
... ∫ ( sin² x cos² x ) dx
= (1/4) ∫ ( 2 sin x cos x )² dx
= (1/4) ∫ sin² 2x dx
= (1/4) ∫ (1/2)[ 1 - cos 2(2x) ] dx
= (1/8) ∫ ( 1 - cos 4x ) dx
= (1/8) [ x - ( sin 4x / 4 ) ] + C
= ( x/8 ) - ( sin 4x / 32 ) + C ................ Ans.
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A Bonus Integral
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... ∫ [ 1 / ( sin² x cos² x ) ] dx
= ∫ [ ( sin² x + cos² x ) / ( sin² x cos² x ) ] dx ... Now Split
= ∫ [ ( 1/ cos² x ) ] + [ 1/ sin² x ) ] dx
= ∫ sec² x dx + ∫ csc² x dx
= tan x - cot x + C ...................... Ans.
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Happy To Help !
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