Math Is Fun Forum

Gotovina

Member

Registered: 2008-02-16

Posts: 8

Improper Integral Type 1

I am stuck on this question, here she is.

Finally the integral I get is

ln(5x+4) - ln(4x+5)

I am confused on the part where I sub in ∞ into the ln's. I get the form ∞ - ∞, I am not sure what to do with this.

TheDude

Member

Registered: 2007-10-23

Posts: 361

Re: Improper Integral Type 1

Combine the logarithms:
ln(a) - ln(b) = ln(a / b)

So in this case you'll get
ln(5x+4) - ln(4x+5) = ln( (5x+4) / (4x+5) )

Now you can take the limit as x approaches infinity and get a meaningful answer.

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Wrap it in bacon

Gotovina

Member

Registered: 2008-02-16

Posts: 8

Re: Improper Integral Type 1

Ahhh, I totally forgot about that thanks. So I think the final answer is ln(5/4).