0:00 / 0:00

Integral Test

Consider the series n=Nan\sum\limits^\infty_{n=N}a_n, where ana_n is a sequence of positive terms.
Let f(n)=anf(n)=a_n and assume that ff is continuous, positive and decreasing.
Then

1. Nf(x)  ⁣dx{\displaystyle\int}^\infty_Nf(x)\de{x} converges if and only if n=Nan\sum\limits^\infty_{n=N}a_n converges.

2. Nf(x)  ⁣dx{\displaystyle\int}^\infty_Nf(x)\de{x} diverges if and only if n=Nan\sum\limits^\infty_{n=N}a_n diverges.

Identifying Clues

  • The terms ana_n look integrable
Determine whether n=13nen2\sum\limits^\infty_{n=1}\frac{3n}{e^{n^2}} converges or diverges.

Practice Question

Determine whether n=3lnnn\sum\limits^\infty_{n=3}\frac{\ln n}{n} converges or diverges.

Extra Practice