MCQ
$\int(x-1) e^{-x} d x$ is equal to
  • A
    $(x+1) e^{-x}+C$
  • B
    $-x e^{-x}+C$
  • C
    $(x-2) e^{-x}+C$
  • D
    $x^{-x}+C$

Answer

(b) $- xe ^{-x}+C$
$
\begin{array}{l}
\text { Explanation: } I=\int(x-1) e^{-x} \\
=\int xe^{-x} dx-\int e^{-x} dx \\
=-xe^{-x}-\int 1 \cdot(-) e^{-x} dx-\int e^{-x} dx+c \\
=-xe^{-x}+\int e^{-x} dx-\int e^{x} dx+c \\
=-xe^{-x}+C
\end{array}
$

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