[tex]\int e^{-4x} dx\\ = \int e^x *e^{-3x}[/tex] let u=e^x so du=e^x dx(adsbygoogle = window.adsbygoogle || []).push({});

so [tex]\int u^{-3} du[/tex]

=[tex] -\frac{1}{2}e^{-2x}+c[/tex]

Thanks,

Casey

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# Homework Help: Can someone confirm this U sub is legal?

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