Formulas

Question 1

What is the notation for finding the value of a certain term in a series of numbers?

EX.

In a sequence of terms in which each term is three times the previous term, what is the fourth term?

Answer 1

An = 3n
A1 = 3(1) = 3
A2 = 3(2) = 6
A3 = 3(3) = 9

If I am asked the 12th term subtracted from the 18th term, it becomes easy.

Question 2

In a recursive sequence, the problem will give you the value of some nth term in the distant future and ask for the value of some earlier/later term in that series. How do you solve?

EX. If An = 2a(n-1) - 4 AND the sixth term = -4
pg 83 Algebra

Answer 2

Use the given value of the term and plug it into the given equation. Work forward/backward until you can find the correct value.

-4 = 2A(6-1) - 4

Question 3

FORMULA TRICK:

What is the value of the 50th term in an arithmetic sequence where first number is -5, second is -3?

Answer 3

Formula = N = -5 + (2n)
BUT remember -5 is the value of the 0 term, and -3 is the value of the 1st term. Therefore, you need to either update the formual = -5 + (2*(n-1)) or remember that the 50th term would be found by plugging in 49.

See pg. 85 Algebra #10 for example.