## Multivariable Calculus, 7th Edition

The values in the sequence are getting smaller and smaller in a geometric sequence. When we divide consecutive terms, we see we have a common ratio of -1/5. We can use the formula $S_{y}=a/(1-r)$, where a is the first term and r is the ratio between terms. When we plug in $a=10$ and $r=-1/5$, we get: $S_{y}=10/(1--1/5)=10/(6/5)=50/6=25/3$