The first term of this series (a+1) is 1 and the common ratio (r) is -3.
Thus, the explicit formula is a_n = 1*(-3)^(n-1).
Must check this! suppose we try to calculate the 3rd term. Then n = 3.
a_3 = 1*(-3)^(3-1) = (-3)^2 = 9. This is correct.
Answer:

Step-by-step explanation:
Rule: 

36.36 is thirty-six and thirty-six hundredths.
36.63 is thirty-six and sixty-three hundredths.
The whole parts are the same. They are both 36.
The decimal parts are 0.63 and 0.36.
Sixty-three hundredths is greater than thirty-six hundredths.
Since 0.63 is greater than 0.36, 36.63 is greater.
Answer:
Original price: $
55
Discount percentage: 25
%
Discount: $13.75
Final Price: $41.25