- #1

MathematicalPhysicist

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what is the integral of lnx?

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- Thread starter MathematicalPhysicist
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- #1

MathematicalPhysicist

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what is the integral of lnx?

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- #2

Lonewolf

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Try writing it as 1*ln(x), then integrate by parts. (Should get x*ln(x)-x).

- #3

MathematicalPhysicist

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could you show me the entire way?

- #4

Lonewolf

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∫1*ln(x)dx

du/dx = 1

v = ln(x)

u = x

dv/dx = 1/x

Now, integrating by parts:

∫1*ln(x)dx = u*v - ∫u*dv/dx

= x*ln(x) - ∫dx

= x*ln(x) - x (+ C to be pedantic)

- #5

MathematicalPhysicist

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i got it, thanks.

edit: just one problem should this ∫u*dv/dx=∫1

edit: just one problem should this ∫u*dv/dx=∫1

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- #6

MathematicalPhysicist

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lonewolf i think i am wrong but i need your verification on that.Originally posted by loop quantum gravity

i got it, thanks.

edit: just one problem shouldnt this be ∫u*dv/dx=∫1 ?

- #7

MathematicalPhysicist

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never mind i found my mistake.

- #8

Lonewolf

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Oops, sorry LQG, I wasn't ignoring you intentionally. Glad you figured it out anyway

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