$$$\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n}$$$
Votre saisie
Déterminez $$$\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n}$$$.
Solution
$$$\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n}$$$ is an infinite geometric series with the first term $$$b=1$$$ and the common ratio $$$q=\frac{19}{20}$$$.
By the ratio test, it is convergent.
Its sum is $$$S=\frac{b}{1-q}=20$$$.
Therefore,
$${\color{red}{\left(\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n}\right)}}={\color{red}{\left(20\right)}}$$
Hence,
$$\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n}=20$$
Réponse
$$$\sum_{n=0}^{\infty} \left(\frac{19}{20}\right)^{n} = 20$$$A
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