Nếu t = x^2 thì:

3/20

Nếu \[t = {x^2}\] thì:

\[xf\left( {{x^2}} \right)dx = f\left( t \right)dt\]

\[xf\left( {{x^2}} \right)dx = \frac{1}{2}f\left( t \right)dt\]

\[xf\left( {{x^2}} \right)dx = 2f\left( t \right)dt\]

\[xf\left( {{x^2}} \right)dx = {f^2}\left( t \right)dt\]

Giải thích

Ta có:\[t = {x^2} \Rightarrow dt = 2xdx \Rightarrow xdx = \frac{{dt}}{2}\]

\[ \Rightarrow xf\left( {{x^2}} \right)dx = f\left( {{x^2}} \right).xdx = f\left( t \right).\frac{{dt}}{2} = \frac{1}{2}f\left( t \right)dt\]

Đáp án cần chọn là: B