1 22
12. The sum of the first n terms of series is 3n+ n. Find the nth term of the series and show
that the series is an arithmetic progression. State the value of the first term and the common
difference.
13. In a geometrical progression, the sum of the first two terms is 3, and the sum of the second
and third terms is -6. Find the first term and the common ratio.
14. How many terms of the series 2 - 6 + 18 – 54 + ... are needed to make a total of 1 (1-38)?​