A geometric sequence is a sequence where each term is found by multiplying or dividing the same value from one term to the next. We call this value "common ratio"

Looking at 2, 4, 8, 16, 32 ....... carefully helps us to make the following observation:

Geometric sequence:2, 4,8

to get the common ratio we multiply each term by 2 to get the next term

y=a.b^x

where a is a constant and b is 2 which is the constant ratio

a=1/2

y=(1/2).2^x .........this is the expotential function