Mathematics

Problem

Find the sum of the following series: a.

2 + 6 + 18 + 54 + \dots

to 8 terms b.

5 + 10 + 20 + 40 + \dots

to 10 terms c.

12 + 6 + 3 + 1.5 + \dots

to 10 terms d.

\sqrt{7} + 7 + 7\sqrt{7} + 49 + \dots

to 12 terms e.

6 - 3 + 1\frac{1}{2} - \frac{3}{4} + \dots

to 15 terms f.

1 - \frac{1}{\sqrt{2}} + \frac{1}{2} - \frac{1}{2\sqrt{2}} + \dots

to 20 terms