2017­1­4 geometric sequences 2.notebook
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-Geometric Sequences W.S.
January 04, 2017
2017­1­4 geometric sequences 2.notebook
Today's Onjective: Explicit Formula for
Geometric Sequences
January 04, 2017
2017­1­4 geometric sequences 2.notebook
January 04, 2017
Explicit Formula For Geometric Sequence
an = a1(r)n-1
1st term
nth term
common ratio
ex. 5, 25, 125, 625....
Find the 12th term of the sequence
To find any term in an geometric sequence
an = a1(r)n-1
1) Identify the first term, or a1
2) Find the common ratio
3) Set up and simplify the explicit formula
4) Substitute for n what number term you are trying to find
ex. Find the 10th term of the sequence 6, 12, 24, 48.....
2017­1­4 geometric sequences 2.notebook
Find the explicit formula.
Then find the a13
January 04, 2017
an = a1(r)n-1
­2, 8, ­32, 128....
Write the explicit formula
16, 8, 4, 2, 1,.......
an = a1(r)n-1
2017­1­4 geometric sequences 2.notebook
January 04, 2017
Write an equation for the nth term of the geometric sequence 2, 12, 72, 432, . . ..
Then find a10.
Write an equation for the nth term of the geometric sequence. Then find a7.
8. 1, −5, 25, −125, . . .
9. 13, 26, 52, 104, . . .
10. 432, 72, 12, 2, . . .
11. 4, 10, 25, 62.5, . . .
2017­1­4 geometric sequences 2.notebook
January 04, 2017