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$$ \int \frac {1-\cos x}{(1+\cos x)\sin x} dx$$

I tried to expand the fraction by sin x and substitute t = cos x, so I got $$ \int \frac{(1-t)}{(1+t)(1-t)(1+t)} dt$$ here i could cancel out (1-t)... but what next? I don't know which formula should be used.

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Doesn't the inside reduce to $1/(1+t)^2$? –  Isaac Solomon Nov 23 '12 at 17:17
    
yes, but what then? –  user50222 Nov 23 '12 at 17:22
    
Beside to Issac's comment, can't you solve $\int (1/u^2)du?$ –  Babak S. Nov 23 '12 at 17:24
    
It would be -1/u + c. So... 1/(1+t)^2 should be -1/(1+t) + c... after substitution -1/(1+cos x) + c, but right answer is 1/(1+cos x)... then why? –  user50222 Nov 23 '12 at 17:31
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Check the sign. Using your substitution $t=\cos x$ you should get $$\int \frac{1-\cos x}{\left( 1+\cos x\right) \sin x}dx=-\int \frac{1-t}{ \left( 1+t\right) \left( 1-t^{2}\right) }dt=-\int \frac{1}{\left( 1+t\right) ^{2}}dt$$ –  Américo Tavares Nov 23 '12 at 17:38

1 Answer 1

up vote 2 down vote accepted

Hint: $$\int\frac{1-\cos x}{(1+\cos x)\sin x}dx=\int\frac{1-\cos^2 x}{(1+\cos x)^2\sin x}dx=\int\frac{\sin^2 x}{(1+\cos x)^2\sin x}dx=\int\frac{\sin x}{(1+\cos x)^2}dx$$ Now take $t=\cos x$ as you noted before.

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good idea, thanks :) –  user50222 Nov 23 '12 at 17:37
    
@user50222: Welcome; but I just wrote what Issacs note. :) –  Babak S. Nov 23 '12 at 17:39
    
You are so gracious and humble! +1 –  amWhy Apr 7 '13 at 0:13

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