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Gabytzu13
20

cos(arcctg de x) =x/radical (1+x la patrat)...........(numai x este la patrat)

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balantudor

[latex]\cos (arctg x)\\ y=arctg x \leftrightarrow tg y=x\\ \sin^2 y + \cos^2 y=1/ \cdot \frac{1}{\cos^2 y} \\ tg^2 y+1=\frac{1}{\cos^2 y} \\ x^2+1=\frac{1}{\cos^2 y} \\ |\cos y|=\sqrt{\frac{1}{x^2+1}} \\ \cos(\arctg x)=\sqrt{\frac{1}{x^2+1}} [/latex]

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