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Math

Math Snap

PROBLEM

Fill in each blank.
6+65+625+6125limnan=limnSn=\begin{array}{l} 6+\frac{6}{5}+\frac{6}{25}+\frac{6}{125} \ldots \\ \lim _{n \rightarrow \infty} a_{n}= \\ \lim _{n \rightarrow \infty} S_{n}= \end{array} \square
\square

STEP 1

1. The sequence given is a geometric series.
2. The general form of a geometric series is a+ar+ar2+ar3+ a + ar + ar^2 + ar^3 + \ldots .
3. The sum of an infinite geometric series S S is given by S=a1r S = \frac{a}{1-r} , where r<1 |r| < 1 .

STEP 2

1. Identify the first term a a and the common ratio r r of the series.
2. Determine the limit of the sequence term an a_n as n n \rightarrow \infty .
3. Determine the sum of the infinite series Sn S_n .

STEP 3

Identify the first term a a and the common ratio r r of the series:
The series is 6+65+625+6125+ 6 + \frac{6}{5} + \frac{6}{25} + \frac{6}{125} + \ldots .
The first term a=6 a = 6 .
The common ratio r r is found by dividing the second term by the first term:
r=656=15 r = \frac{\frac{6}{5}}{6} = \frac{1}{5}

STEP 4

Determine the limit of the sequence term an a_n as n n \rightarrow \infty :
The general term of the sequence an=6(15)n1 a_n = 6 \left(\frac{1}{5}\right)^{n-1} .
As n n \rightarrow \infty , the term (15)n10 \left(\frac{1}{5}\right)^{n-1} \rightarrow 0 .
Thus, limnan=0 \lim_{n \rightarrow \infty} a_n = 0 .

SOLUTION

Determine the sum of the infinite series Sn S_n :
The sum of an infinite geometric series is given by:
S=a1r=6115=645=6×54=304=7.5 S = \frac{a}{1-r} = \frac{6}{1-\frac{1}{5}} = \frac{6}{\frac{4}{5}} = 6 \times \frac{5}{4} = \frac{30}{4} = 7.5 Thus, limnSn=7.5 \lim_{n \rightarrow \infty} S_n = 7.5 .
The completed blanks are:
1. limnan=0\lim_{n \rightarrow \infty} a_n = 0
2. limnSn=7.5\lim_{n \rightarrow \infty} S_n = 7.5

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