Question

Find the sum of the first 5 terms of the geometric series 7, 21, 63, …

Answer 1

First step would be to write the equation that produces the series...

Answer 2

What would that look like? I assumed it was the multiplication of three but it wasn't one of the answers given.

Answer 3

Okay, you could just write out the first 5 terms and add them up...that would work here but isn't generally practical. We might as well figure out how to do it in any case. To do that, though, we need the formula that generates the terms in the series.

Multiplying by 3 is a good start, but how to write that?

Answer 4

first term is 7
second term is 7*3 = 21
third term is 7*3*3 = 63
fourth term is ?
fifth term is ?