Exercício 9
Calcule a integral
\[ \int_0^1 \frac{y}{\textrm{e}^{2y}}\,dy. \]
Solução
Como \(\frac{y}{\textrm{e}^{2y}}=y\textrm{e}^{-2y}\), calculamos
\[ \int_0^1 y\textrm{e}^{-2y}\,dy. \]
Usamos integração por partes com
\[ u=y, \qquad dv=\textrm{e}^{-2y}\,dy. \]
Então \(du=dy\) e \(v=-\frac{1}{2}\textrm{e}^{-2y}\). Logo,
\[ \int y\textrm{e}^{-2y}\,dy =-\frac{y}{2}\textrm{e}^{-2y} +\frac{1}{2}\int \textrm{e}^{-2y}\,dy. \]
Portanto,
\[ \int y\textrm{e}^{-2y}\,dy =-\frac{y}{2}\textrm{e}^{-2y}-\frac{1}{4}\textrm{e}^{-2y}. \]
Avaliando de \(0\) até \(1\),
\[ \int_0^1 \frac{y}{\textrm{e}^{2y}}\,dy =\left[-\frac{y}{2}\textrm{e}^{-2y}-\frac{1}{4}\textrm{e}^{-2y}\right]_0^1. \]
\[ \colorbox{green!20}{ \int_0^1 \frac{y}{\textrm{e}^{2y}}\,dy =\frac{1}{4}-\frac{3}{4\textrm{e}^2} }. \]