IMathAS-libretexts

Evaluate the integral: $\displaystyle {\int_{{0}}^{\infty}}{4}{x}{e}^{{-{x}/{9}}}\ {\left.{d}{x}\right.}$

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\displaystyle

Enter your answer as a number (like 5, -3, 2.2172) or as a calculation (like 5/3, 2^3, 5+4)
Enter DNE for Does Not Exist, oo for Infinity