Posted by **Jon** on Wednesday, December 12, 2007 at 3:18pm.

1)Find a1 in a geometric series for which Sn=300,r=-3,and n=4

A)15

B)15/2

C)-15

D)1/15

I chose A

2)Find the sum of the infinite geometric series. Sigma sign with infinity symbol above and n=1 below. To the right 20(-1/4)n-1

A)25

B)80/3

C16

D)does not exist

I chose A

3)Find the sum of the infinite geometric series:4+3+9/4+:...

A)16/7

B)16

C)-12

D)does not exist

I chose B

4)Write 0.72 repeating as a fraction.

A)7/9

B)8/11

C)18/25

D)7 and 2/9

I chose B but my book confuses me on how to work it out. I just divided 8 and 11 and I got .72 repeating

5)Find the fifth term of the sequence in which a1=-3,and aN+1=3aN-n

A)-301

B)-99

C)-193

D)-341

I don't know

- math -
**Damon**, Wednesday, December 12, 2007 at 5:23pm
1. I chose B

2. C

3. Hey, I better start showing you how

1. Plain geometric series

Sn = g(1-r^n)/(1-r)

300 = g (1-3^4) /1-3

300 = g (1-81) / -2

g = 300 (-2/-80)

g = 15/2

2. sigma = g/(1-r)

g=20

r=-1/4

sigma = 20/1.25

= 2000/125

= 400/25

= 16

3. g = 4

r = 3/4

s = 4/(1-3/4)

=16

4. .72 72 72 72 ....

= 72 10^-2 + 72 10^-2 10^-2 +72 (10^-2)^3 ...

this is geometric series with

g = 72*10^-2

r = 10^-2

so

s = 72*10^-2/(1-.01)

= .72/.99

= 8/11

I do not understand the last one.

- math -
**Jon**, Wednesday, December 12, 2007 at 5:43pm
thanks for the help. are you possitive they are correct?

- math -
**Damon**, Wednesday, December 12, 2007 at 5:48pm
Oh good heavens, always check anything I do!

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