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Provide Solution for RD Sharma Class 12 Chapter 19 Definite Integrals Exercise Revision Exercise Question 18

Answers (1)

Answer:   \frac{\sqrt{e}-1}{e}

Given:  \int_{1}^{2} \frac{1}{x^{2}} e^{-\frac{1}{x}} d x

Hint: Use Substitution method

Solution:

Let

\begin{aligned} &\frac{-1}{x}=t \\ & \end{aligned}                  (Differentiating w.r.t to x)

\frac{1}{x^{2}} d x=d t

\begin{aligned} &\int_{1}^{2} \frac{1}{x^{2}} e^{-\frac{1}{x}} d x\\ & \end{aligned}

\int_{1}^{2} e^{t} d t=\left(e^{t}\right)_{1}^{2}=\left(e^{\frac{-1}{x}}\right)_{1}^{2}\\

\begin{aligned} &=e^{\frac{-1}{2}}-e^{-1} \\ \end{aligned}

=e^{-\frac{1}{2}}-\frac{1}{e} \\

=\frac{\sqrt{e}-1}{e}

 

 

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