We often use integrals of the functions
, for various values of p, to help determine whether other integrals converge or diverge.
You already did the work to show this, so we'll just summarize the results. Assuming p is greater than 0 (because otherwise the exponents do weird things),
converges if p < 1 and diverges otherwise.
converges if p > 1 and diverges otherwise.
This is often called the p-test for improper integrals.
Practice:
Use the <em>p</em>-test to determine if 
converges or diverges. | |
Since the integrand is of the form where p > 1 and the interval of integration is [0,1], this integral diverges. Piece of cake, right? The hard part is remembering when you want p > 1 and when you want p < 1. There's a great trick for that: you can get by with remembering just one integral. The integral 
converges because gets close to the x-axis quickly as x approaches ∞. If you can remember this, then you can remember that 
because you have an example where p = 2 is greater than 1 and the integral converges. That means 
We switch between p > 1 and p < 1 when we change the interval of integration from [1,∞) to [0,1], so this means 
and 
That's the whole p-test, and all we had to remember was that the integral 
converges. We recommend taking your time when using the p-test. It can be easy to get mixed up, even if you know what you're doing! | |
Use the p-test to determine if the integral converges or diverges.

Answer
The integral

diverges because the integrand is of the form
with p > 1 and we're integrating from 0 to 1.
Use the p-test to determine if the integral converges or diverges.

Answer
The integral

is of the form
with p < 1, so this integral converges.
Use the p-test to determine if the integral converges or diverges.

Answer
The integral

converges because the integrand is of the form
with p > 1 and we're integrating from 1 to ∞.
Use the p-test to determine if the integral converges or diverges.

Answer
The integral
is of the form

where p < 1, so this integral diverges.