Sandra has a $20 itunes gift card and spends $3 each month. Which of the following functions models how much money Sandra has on her gift card after x months?

x3-20

Step-by-step explanation:

x stands for the month 3 is the money that she is spending each month if you multiply those together you get the amount of money she has spent over x amount of months minus the 20 dollars on her gift card

hello from mrbilldoesmath!

answer:

a(n) - a(n-1) -3

discussion:

this ones a bit interesting. given a(n) = 5 - 3n consider this:

a(n-1) = 5 - 3(n-1)

          = (5 - 3n) + 3             => but a(n) = 5 - 3n, the first term

          = a(n)   + 3                 => subtract 3 from both sides

a(n-1) -3 = a(n)  

or

a(n) - a(n-1) -3

you,

mrb