∫
x
f
′
(
x
)
d
x
\int xf{'}(x)\,{\rm d}x
∫xf′(x)dx
=
∫
x
d
f
(
x
)
=\int x\,{\rm d}{f(x)}
=∫xdf(x)
=
x
f
(
x
)
−
∫
f
(
x
)
d
x
=xf(x)-\int f(x)\,{\rm d}x
=xf(x)−∫f(x)dx
由题知:
f
(
x
)
=
(
ln
2
x
)
′
=
2
ln
x
×
1
x
=
2
ln
x
x
f(x)=({\ln}{^2} x){'}=2\ln x\times\frac{1}{x}=\frac{2\ln x}{x}
f(x)=(ln2x)′=2lnx×x1=x2lnx
原式
=
2
ln
x
−
ln
2
x
+
C
=2\ln x-\ln^2 x+C
=2lnx−ln2x+C