# What is the sum of the infinite geometric series with a_1=42 and r=6/5?

That is a tricky question because a geometric series converges only when $\left\mid r \right\mid < 1$. Here we have $\left\mid r \right\mid = \left\mid \frac{6}{5} \right\mid = \frac{6}{5} = 1 \frac{1}{6} > 1$.