1. 11.5 Arithmetic and Geometric Series

2. Sum of the first n terms of Arithmetic Series
n = # of terms
t1 = 1st term
tn = nth term
Ex) Find the sum of the first 40 terms (S40) of the Arithmetic Series: …
Find the 40th term:
t1 = d = 3
Find the sum:

3. Ex) Evaluate First expand the series to get t1 and t20: (5(1)+2) + …
+ (5(20)+2)
7 + … + 102
Find S20:

4. Sum of first n terms of Geometric Series (new formula)
n = # of terms
t1 = 1st term
r = common ratio
Ex) Evaluate:
Expand: (don’t need last term in geo, yay!)
+ …
3 + …
t1 = 3
n = 10
Find r: r

5. Sum of first n terms of Geometric Series
n = # of terms
t1 = 1st term
r = common ratio
t1 = 3
n = 10
r = -2
exponents first!!

6. YOYO- find S9 for the Geo. Series with
Clue: It’s a BIG
number
t1 = 5
r = -3

7. A Partial Sum is given, find n.
Arithmetic Series, Sn = 4859, t1=8 d = 5
Find n (Need Quad. Formula for Arith)

8. A Partial Sum is given, find n.
Geo. Series, Sn  , t1= 47 r = 1.06
Find n. (Need Logs for Geo)

9. Homework
Pg Q1-10, 1 – 31 odd