Statements on series

[alex_cortney]

Which of the following statements from the screenshot on series is correct? A and B are naturally incorrect; C is correct, and I am completely not sure what to do with D and how even to start there. Can you please help? Thank you in advance!

 

[lex]

What about doing the ratio test?

 

[nasi112]

(d) Since [MATH]\sum_{n=1}^{\infty} a_n \ [/MATH] diverges.

What can you say about? [MATH]\sum_{n=1}^{\infty} \frac{1}{a_n} \ [/MATH]?