Question

tính :

\(\int\)e^2x. sin²xdx

 

Answer 1

\(\int e^{2x}.sin^2xdx\).

Đặt \(\left\{{}\begin{matrix}u=sin^2x\\dv=e^{2x}dx\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}du=2sinxcosxdx=sin2xdx\\v=\dfrac{1}{2}e^{2x}\end{matrix}\right.\).

\(\Rightarrow\) \(\int e^{2x}.sin^2xdx=\dfrac{e^{2x}.sin^2x}{2}-\dfrac{1}{2}\int e^{2x}.sin2xdx\) (1).

Đặt \(\left\{{}\begin{matrix}u=sin2x\\dv=e^{2x}dx\end{matrix}\right.\Rightarrow\left\{{}\begin{matrix}du=2cos2xdx=2\left(1-2sin^2x\right)dx\\v=\dfrac{1}{2}e^{2x}\end{matrix}\right.\).

\(\Rightarrow\) \(\int e^{2x}.sin2xdx=\dfrac{1}{2}e^{2x}.sin2x-\int e^{2x}.\left(1-2sin^2x\right)dx=\dfrac{e^{2x}.sin2x-e^{2x}}{2}+2\int e^{2x}.sin^2xdx\) (2).

Thế (2) và (1), ta suy ra:

\(\int e^{2x}.sin^2xdx=\dfrac{1}{8}e^{2x}.\left(2sin^2x-sin2x+1\right)+C\).