Identify whether the series sigma notation infinity i=1 15(4)^i-1 is a convergent or divergent geometric series and find the sum, if possible

a This is a divergent geometric series. The sum is –5.
b This is a convergent geometric series. The sum is –5.
c This is a divergent geometric series. The sum cannot be found.
d This is a convergent geometric series. The sum cannot be found.

Question

Identify whether the series sigma notation infinity i=1 15(4)^i-1  is a convergent or divergent geometric series and find the sum, if possible

a   This is a divergent geometric series. The sum is –5. 
b   This is a convergent geometric series. The sum is –5. 
c   This is a divergent geometric series. The sum cannot be found. 
d   This is a convergent geometric series. The sum cannot be found.

anonymous · Answer

$$\sum_{i=1}^{\infty} 15(4)^{i-1}$$

experimentx · Answer

that's a geometric series ... with common ratio 4 which is greater than 1 ... so it diverges

anonymous · Answer

So, c because you cannot find the sum of a divergent geometric series.  correct?