How to find an exponential function with two points?

Well u have a basic equation y=a • b^x
a is the initial amount
b is the growth factor
and x is the exponent

the first step is to make a chart with ur two points for example
(0,4) and (2,16)
so ur chart will be
x. | y.
0. | 4
2. | 16
next you find the difference between the x side so 0 to 2 is +2
then find the difference between the y side so 4 to 16 is +12
then put it into a fraction with y over x or y/x so 12/2 then simplified 6/1 or just 6.

6 is the growth factor
and to find a u have to go on the y column and find the first number so
a is 4
x is still x because it's 0 but if it was 2 then it would be x-2 so it can cancel
so the answer would be y=4 • 6^x

Cthe residual plot for model 1 has a non random pattern and is a good fit for the data