What is the sum of the next three terms in the geometric sequence 1, 2, 4, ...?
Since it is a geometric sequence, ask yourself "What number times 1 will give you 2?" ---> 2
Again: "What number times 2 will give you 4?" ---> again, the answer is 2.
So, this is your common ratio; you can find all the rest of the terms by multiplying each preceding term by 2.