Algebra
posted by Becca on .
Two questions I need help with.
Find the indicated partial sum using the information given.
1. a3=4/9, a7=9/64, S6
Determine wheater the infinite geometric series has a finite sum
2. 6+ 3+ 3/2 + 3/4 +....
3. 49 + (7) + ( 1/7) +...

1. S6 = 6/2(a+5d)
d = (A7A3)/4
a = A32d
2. since r = 1/2 < 1, yes the sum is finits
3. same 
I will assume that by a3 you mean term(3)
and the terms form an geometric sequence
term(3) = ar^2 = 4/9
term(7) = ar^6 = 9/64
divide term7 by term3
r^4 = (9/64) / (4/9) = 81/256
r = ± 3/4
the in ar^2 = 4/9
a(9/16) = 4/9
a = 64/81
so Sum(6) = a(r^6  1)/(r1)
= (64/81)((3/4)^6  1)/(3/4  1)
= 3367/1296
= appr 2.59799
2. term2/term1 = 1/2
term3/term2 = 1/2
since r < 1 , the infinite series has a finite sum
2nd one:
r = 7/49 = 1/7
yes, so does that one