Converging or diverging integral

Calculus Level 3

Does the following integral converge or diverge?

0 arctan ( x ) e x + 1 d x \int^\infty_0 \frac{\arctan{(x)}}{e^x+1} \, dx

Converge Diverge

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

1 solution

Joe Plaza
Mar 4, 2016

We will use the comparison theorem to prove this. Let f ( x ) = arctan ( x ) e x + 1 f(x) =\frac{\arctan{(x)}}{e^{x}+1} We know the maximum value arctan ( x ) \arctan{(x)} can take is π 2 \frac{\pi}{2} , therefore we can set an upper bound of f ( x ) f(x) as π 2 e x + 2 \frac{\pi}{2e^x + 2} . If we can prove that this is less than a function g ( x ) g(x) for all x > 0 x>0 then we have consequently shown that f ( x ) < g ( x ) f(x) < g(x) for all x > 0 x>0 . If this is the case, and if g ( x ) g(x) converges, then f ( x ) f(x) must also converge. We now let g ( x ) = π e x g(x) = \frac{\pi}{e^{x}} , since we know 0 π e x = π \int_{0}^{\infty}\frac{\pi}{e^{x}} = \pi . Now with a little rearranging, it is clear that π 2 e x + 2 < π e x \frac{\pi}{2e^x + 2} < \frac{\pi}{e^x} and therefore the integral must converge.

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...