hi, i have to integrate the following problem by parts. i started to do it, but then i got stuck halfway through. if anyone could show me how it is done, i would be grateful.

INT (square root of y) * (ln(y)) dy

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- Feb 3rd 2007, 07:42 PMclockinglyintegration by parts
hi, i have to integrate the following problem by parts. i started to do it, but then i got stuck halfway through. if anyone could show me how it is done, i would be grateful.

INT (square root of y) * (ln(y)) dy - Feb 3rd 2007, 08:09 PMAfterShock
- Feb 3rd 2007, 08:10 PMThePerfectHacker
- Feb 3rd 2007, 08:13 PMticbol
By parts.

INT.[u]dv = u*v -INT.[v]du -------(i)

INT.[sqrt(y) *ln(y)]dy -------------(1)

You can try two ways. I did, and I found this is the correct assumption.

Let u = ln(y)

Hence, du = (1/y)dy

And so, dv = sqrt(y) dy = (y^(1/2))dy

Hence, v = 1/(3/2) *y^(3/2) = (2/3)y^(3/2)

INT.[sqrt(y) *ln(y)]dy -------------(1)

Apply the assumptions, and (i),

= ln(y)*[(2/3)y^(3/2)] -INT.[(2/3)y^(3/2)][(1/y)dy]

= (2/3)(y^(3/2))ln(y) -(2/3)INT.[y^(1/2)]dy

= (2/3){y^(3/2) ln(y) -(2/3)(y^(3/2))} +C

= [(2/3)y^(3/2)]{ln(y) -2/3} +C

= (2/3)(y)(sqrt(y))[ln(y) -2/3] +C --------------answer.

= [ln(y) *(2/3)y^(3/2)] -