What are the 5 terms of each geometric sequence

In #17, the first term is 2 and the second is 10.  10 is 5 times 2.  Checking further, you will conclude that the "common ratio" is 5.

Then a_(n) = 2*5^(n-1), with n beginning at 1. 

Check:  what is a1?  It's 2*5^(1-1) = 2, which is what we expected.
What is the 3rd term?  It's 2*5(3-1) = 2*5^2 = 50, which is what we expected.

A= b/2 because u simplying both sides of equation