(cosx-1)/sinx + sinx/(cosx +1) =?
[tex]\it E = \dfrac{\cos x-1}{\sin x} + \dfrac{\sin x}{\cos x+1} = \dfrac{(\cos x-1)(\cos x+1)+sin^2x}{sin x(\cos x+1)}=
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= \dfrac{\cos ^2x - 1 +sin^2x}{sin x(\cos x+1)}= \dfrac{\cos ^2x +sin^2x -1}{sin x(\cos x+1)}= \dfrac{ 1- 1 }{sin x(\cos x+1)}= 0[/tex]
