Does the following infinite series converge or diverge? Explain your answer. 1/5 + 1/15 + 1/45 + 1/81...

A.It diverges; it has a sum.


B.It converges; it does not have a sum


C.It diverges; it does not have a sum.


D.It converges; it has a sum.

Respuesta :

It converges; it has a sum.

Answer with explanation:

The given series is

 [tex]\frac{1}{5}+\frac{1}{15}+\frac{1}{45}+\frac{1}{81}+.....[/tex]

The given series is a geometric sequence,whose common ratio is equal to

  [tex]R=\frac{2^{nd}\text{term}}{1^st \text{term}}\\\\R=\frac{\frac{1}{15}}{\frac{1}{5}}\\\\R=\frac{5}{15}\\\\R=\frac{1}{3}[/tex]

Sum to Infinity is given by the formula

           [tex]S_{\infty}=\frac{\text{First term}}{1-\text{Common ratio}} \text{or}\frac{\text{First term}}{\text{Common ratio}-1} \\\\S_{\infty}=\frac{\frac{1}{5}}{1-\frac{1}{3}}\\\\S_{\infty}=\frac{\frac{1}{5}}{\frac{2}{3}}\\\\S_{\infty}=\frac{3}{10}[/tex]

As the sum of series is Finite, that is having a single value, so the series is Convergent.

If it has more than one sum, it would have been Divergent.

Option D: It converges; it has a sum.