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Integrals

Question
CBSEENMA12032472

Evaluate the following integral:
integral subscript 1 superscript 2 1 over straight x squared straight e to the power of negative 1 over straight x end exponent dx



Solution

Let I = integral subscript 1 superscript 2 1 over straight x squared straight e to the power of 1 over straight x end exponent dx
Put 1 over straight x space equals straight y comma space space space space space space therefore space space minus 1 over straight x squared dx space equals space dy space space space space space space space space space space rightwards double arrow space space space 1 over straight x squared dx space space equals negative dy
When x = 1,   y = 1
When x  =2,   y = 1 half
therefore space space space straight I space space equals negative integral subscript 1 superscript 1 half end superscript space straight e to the power of straight y space dx equals space minus open square brackets straight e to the power of straight y close square brackets subscript 1 superscript 1 half end superscript space equals space minus open square brackets straight e to the power of 1 half end exponent minus straight e to the power of 1 close square brackets space equals space straight e minus square root of straight e

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