integration

Calculus Level 3

find I


The answer is 0.63629.

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4 solutions

Antony Diaz
Mar 7, 2015

1 2 e l n x l n x d x = 1 2 x l n x d x = 1 2 x 2 ( 2 l n x 1 ) 4 = ( 2 2 ( 2 l n 2 1 ) 4 ) ( 2 l n 1 1 4 ) = 2 l n 2 1 1 4 0.636 \int _{ 1 }^{ 2 }{ { e }^{ ln\quad x }\cdot ln\quad x } \quad dx\\ =\int _{ 1 }^{ 2 }{ x\cdot ln\quad x } \quad dx\\ =\int _{ 1 }^{ 2 }{ \cfrac { { x }^{ 2 }(2\cdot ln\quad x\quad -1) }{ 4 } } \\ =(\cfrac { { 2 }^{ 2 }(2ln\quad 2\quad -1) }{ 4 } )-(\cfrac { 2ln\quad 1\quad -1 }{ 4 } )\\ =2ln\quad 2\quad -1-\cfrac { 1 }{ 4 } \\ \approx 0.636\\

Hari Eeshwar
Apr 18, 2015

As we know, (x(e^x))`=(e^x)(1+x) By deducing this one to that form we get : (e^(ln(x))) ln(x) = (1/2)((e^(2ln(x))) (1+2ln(x))) - (1/2)((e^(2ln(x))) By integrating the RHS, We get: I = { [ln(x) (x^2)/2] - (x^2)/4 } between the limits 2 and 1 By further solving, we get 0.6362.

e^lnx=x ,so I changes to xlnx ,now integrate by parts to get the value .6346

yes good one for Jee mains!

Jitendra Kumar Routray - 6 years, 2 months ago
Anupam Khandelwal
Mar 29, 2015

One can also use Integration by Parts and then substitute the limits .

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