Answer
$\displaystyle\sum_{i=0}^{2}\left(-\dfrac{3}{2}\right)^i$
Work Step by Step
Using the summation symbol, the expression $
1+\left(-\dfrac{3}{2}\right)+\dfrac{9}{4}
$ can be written as
\begin{array}{l}
\displaystyle\sum_{i=0}^{2}\left(-\dfrac{3}{2}\right)^i
\end{array}