Write the sum using summation notation, assuming the suggested pattern continues.

2 - 12 + 72 - 432 +

 

The first term is a = 2. The common ratio is r = -6. You start off with 2 and multiply each term by -6 to get the next term. 

eg: 2*(-6) = -12 ---> -12*(-6) = 72 etc etc

If you want the series summation to go on forever, then replace the 'n' up top with the infinity symbol 

Note: Because |r| < 1 is not true (r < 1 in this case), this means that the series diverges.

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