Integration By Parts (Logarithm) int(2x+3)ln (x)dx

goorst9Bi

goorst9Bi

Answered question

2022-11-24

Integration By Parts (Logarithm)
( 2 x + 3 ) ln ( x ) d x
My attempts,
= ( 2 x ln ( x ) + 3 ln ( x ) ) d x
= 2 x ln ( x ) d x + 3 ln ( x ) d x
For x ln ( x ), integrate by parts,then I got
= x 2 ln ( x ) ( x ) d x + 3 ln ( x ) d x
= x 2 ln ( x ) x 2 2 + 3 ln ( x ) d x
For ln ( x ), integrate by parts, then I got
= x 2 ln ( x ) x 2 2 + 3 x ln ( x ) 3 1 d x
= x 2 ln ( x ) x 2 2 + 3 x ln ( x ) 3 x + c
= 1 2 x ( x + 2 ( x + 3 ) ln ( x ) 6 ) + c
But the given answer in book is x 2 ln ( x ) x 2 2 + 3 x + c. What did I do wrong?

Answer & Explanation

skilningugdK

skilningugdK

Beginner2022-11-25Added 15 answers

Bookish answer is wrong:
( x 2 ln ( x ) x 2 2 + 3 x + c ) = 2 x log x 3 x 2
And yours:
( 1 2 x ( x + 2 ( x + 3 ) ln ( x ) 6 ) + c ) = 2 x log x + 3 log x = ( 2 x + 3 ) log x
e3r2a1cakCh7

e3r2a1cakCh7

Beginner2022-11-26Added 2 answers

Try this way:
( 2 x + 3 ) ln x   d x = ln x ( 2 x + 3 )   d x [ d ( ln x ) d x ( 2 x + 3 )   d x ] d x

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