# How do you find the sum of the first 12 terms of 4 + 12 + 36 + 108 + ?

##### 1 Answer

Mar 18, 2016

this is a geometric

first term is a = 4

2nd term is mult by 3 to give us 4(

3rd term is 4(

4rth term is 4(

and the 12th term is 4(

so a is 4 and the common ratio (r) is equal to 3

that's all you need to know.

oh, yeah, the formula for the sum of the 12 terms in geometric is

substituting a=4 and r=3, we get:

you can confirm this formula is true by calculating the sum of the first 4 terms and comparing

works like a charm. All you have to do is figure out what the first term is and then figure out the common ratio between them!