# Ratio test - Sequence and series

### Ratio test

In this lesson, we will learn about the ratio test. This test requires you to calculate the value of R using the formula below. If R is greater than 1, then the series is divergent. If R is less than 1, then the series is convergent. If R is equal to 1, then the test fails and you would have to use another test to show the convergence or divergence of the series. It is really recommended to use this test if your series has factorials in it. We will do a few questions which involve using the ratio test, and then look at a question that requires us to use the ratio test twice.