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Cat este [tex] \int\limits^._. { \frac{x}{ x^{2} +1} } \, dx [/tex] ?

Răspuns :

x²+1=t
2xdx=dt
[tex]1/2 \int\ { \frac{2xdx}{ x^{2} +1} } \, dx = \frac{1}{2} \int\ { \frac{dt}{t} } \,= [/tex]=
=1/2lnItI+c=1/2ln(x²+1)+c