How do you integrate e^(-x)dxexdx?

1 Answer
Apr 26, 2016

-e^-x+Cex+C

Explanation:

We will use the following integral rule:

inte^udu=e^u+Ceudu=eu+C

Thus, to integrate

inte^-xdxexdx

We set u=-xu=x. Thus, we have:

color(red)(u=-x)" "=>" "(du)/dx=-1" "=>" "color(blue)(du=-dx)u=x dudx=1 du=dx

Since we have only dxdx in the integral and not -dxdx, multiply the interior of the integral by -11. Balance this by multiplying the exterior by -11 as well.

inte^-xdx=-inte^color(red)(-x)color(blue)((-1)dx)=-inte^color(red)ucolor(blue)(du)exdx=ex(1)dx=eudu

This is the rule we knew originally. Don't forget that the integral is multiplied by -11:

-inte^udu=-e^u+C=barul|color(white)(a/a)-e^-x+Ccolor(white)(a/a)|