View Full Version : An analytic solution?
SW VandeCarr
Apr7-10, 10:39 PM
Is there an analytic solution to the following integral? (Not a homework question, solved numerically).
\int_{0}^{\infty}{\frac{dx}{(1+x)\sqrt{x}}=\pi
l'Hôpital
Apr7-10, 11:50 PM
Let u^2 = x
SW VandeCarr
Apr8-10, 12:59 AM
Let u^2 = x
OK I get: 2\int\frac{1}{1+u^2}du
I'm a bit rusty at this. I think I need to make some trig substitutions here, but I'm at a loss as to exactly what.
jrlaguna
Apr8-10, 04:06 AM
It's just there, the arc tangent.
SW VandeCarr
Apr8-10, 12:21 PM
It's just there, the arc tangent.
Right. I finally saw that. However, the solution: 2\arctan(\sqrt{x})+C contains a variable. The solution given in the CRC Standard Mathematical Tables 14th ed, page 342, Eq 489 is \pi.
EDIT:Yes, I know it's old, but I doubt a new solution has been invented. I bought it for $2.
You looked up the indefinite integral. You have a definite integral. Apply the integration limits.
SW VandeCarr
Apr8-10, 01:51 PM
You looked up the indefinite integral. You have a definite integral. Apply the integration limits.
The form of the integral in the book is just as I wrote it in the first post, but I see how the solution \pi is obtained. Thanks.
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