\( \int x e^{-x} d x \)
Evaluate the integral: \(\int x e^{-x} d x = -x e^{-x} + e^{-x} + C\)
Step 1 :Perform integration by parts: let \(u=x\) and \(dv=e^{-x}dx\), then \(du=dx\) and \(v=-e^{-x}\)
Step 2 :Apply the integration by parts formula: \(\int x e^{-x} d x = -x e^{-x} - \int(-e^{-x})dx\)
Step 3 :Evaluate the integral: \(\int x e^{-x} d x = -x e^{-x} + e^{-x} + C\)