Question

Integrate xe^(-x^2).

Answer 1

You can easily integrate it using a simple substitution:

$\large\begin{array}{l} \mathsf{\displaystyle\int\!x\,e^{-x^2}\,dx}\\\\ =\mathsf{\displaystyle\int\!\left(-\frac{1}{2}\right)\cdot (-2)x\,e^{-x^2}\,dx}\\\\ =\mathsf{\displaystyle-\,\frac{1}{2}\int\!\,e^{-x^2}\cdot (-2x)\,dx\qquad\quad(i)}\\\\ \end{array}$


$\large\begin{array}{l} \textsf{Let}\\\\ \mathsf{-x^2=u,}\quad\textsf{then}\quad\mathsf{-2x\,dx=du}\\\\\\ \textsf{so (i) becomes}\\\\ =\mathsf{\displaystyle-\,\frac{1}{2}\int\!e^u\,du}\\\\ =\mathsf{\displaystyle-\,\frac{1}{2}\cdot e^u+C}\\\\ =\mathsf{\displaystyle-\,\frac{1}{2}\cdot e^{-2x}+C}\\\\\\ \boxed{\begin{array}{c} \mathsf{\displaystyle\int\!x\,e^{-x^2}\,dx=-\,\frac{1}{2}\,e^{-x^2}+C} \end{array}}\qquad\checkmark \end{array}$


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$\large\textsf{I hope it helps. :-)}$


Tags: integrate substitution indefinite integral exponential composite calculus