Is the sequence 3,12,36, a geometric sequence? explain

A geometric sequence goes from one term to the next by always multiplying (or dividing) by the same value. So 1, 2, 4, 8, 16, ... and 81, 27, 9, 3, 1, 1/3, ... are geometric, since you multiply by 2 and divide by 3, respectively, at each step.

Your problem doesnt have this pattern.