# How do you find the sum of the infinite geometric series -10,-5,-5/2?

Sum $= - 20$

#### Explanation:

The formula ${S}_{\infty} = {a}_{1} / \left(1 - r\right)$

${a}_{1} = - 10$ and $r = \frac{1}{2}$

${S}_{\infty} = - \frac{10}{1 - \frac{1}{2}}$

${S}_{\infty} = - 20$

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