how many terms are in the arithmetic sequence 5, 1, −3, …, −99?

There are 26 terms in this arithmetic sequence. They are all subtracted by 4.

The common difference = 1 -5 = -4

nth term  = 5 +(n-1)*-4 
last term = -99 :-
-99 = 5 -4n + 4 
-99 = 9 - 4n
4n =  108
n = 27

there are 27 terms in this series

Area of circle = pi * radius^2radius is given to be 1/2 inchespi * (1/2)^2 = pi/4 inches^2 = 0.785 inches^2