Suppose your 4 has a special checking account used just for paying the phone bill. The balance is $740.00 this month. Next month the balance will be $707.60, after that it will be $675.20, and on the third month the balance will be $642.80. Write an explicit formula to represent the balance in the account as an arithmetic sequence. How many months can you pay your phone bill without depositing any more money in the account?

dа ta:

a₁=740

a₂=707.6

a₃=675.2

a₄=642.8

We use to find any term of an arithmetic sequence this equiation:

an=a₁ + (n-1) d

a₁ = is the first term

n=is the number of the term to find.

d=is de common diference.

d=an - (an-1)

d=a₂-a₁=707.6 - 740=-32.4

Then:

an=740-32.4 (n-1)

an=740-32.4n+32.4

an=-32.4n+772.4

Now, how many months can I pay my phone bill depositing any more meney in the account?

n=numbers of months tha I can pay my phon bill.

an=0

0=-32.4n+772.4

32.4n=772.4

n=772.4 / 32.4=23.8≈23

I can pay 23 months without depositing more money in the account.