sum from n=2 to infinity of 3/(7^n)

Lösung

n = 2 \sum \infty \frac{3}{7 ^{n}}

\frac{1}{14}

Dezimale

0.07142 \dots

Schritte zur Lösung

n = 2 \sum \infty \frac{3}{7 ^{n}}

Wende die Regel der konstanten Multiplikation:

\sum c \cdot a_{n} = c \cdot \sum a_{n}

= 3 \cdot n = 2 \sum \infty \frac{1}{7 ^{n}}

n = k \sum \infty (a_{n}) = n = 0 \sum \infty (a_{n}) - a_{0} - a_{1} - \dots a_{k - 1}

= 3 (n = 0 \sum \infty \frac{1}{7 ^{n}} - \frac{1}{7 ^{0}} - \frac{1}{7 ^{1}})

n = 0 \sum \infty \frac{1}{7 ^{n}} = \frac{7}{6}

= 3 (\frac{7}{6} - \frac{1}{7 ^{0}} - \frac{1}{7 ^{1}})

Vereinfache

3 (\frac{7}{6} - \frac{1}{7 ^{0}} - \frac{1}{7 ^{1}}) : \frac{1}{14}

= \frac{1}{14}

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