math
posted by Jon on .
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
5)Find the fifth term of the sequence in which a1=3,and aN+1=3aNn
A)301
B)99
C)193
D)341
I don't know

Jon, for #1 the equation is
300 = a((3)^4  1)/(31)
300 = a(80)/4
a = 15
since there are only 4 terms, this is easy to check
15 + 45 + (135) + 405 = 300
for you #2, I will assume you meant
a_{1} = 3
a_{N+1} = 3_{N}  n
then:
a_{1} = 3
a_{2} = 3a_{1}  2 = 11
a_{3} = 3a_{2}  3 = 36
a_{4} = 3a_{3}  4 = 112
a_{5} = 3a_{4}  5 = 341 which is choice D 
find a1 for given geometric series.
Sn= 405, r=3, n=4