Question #d27c8

1 Answer
Mar 21, 2016

a. sum_(n=0)^oo 0.4^n =5/3n=00.4n=53

b. sum_(n=1)^oo(-0.1)^n/3=-1/33n=1(0.1)n3=133

Explanation:

A geometric series is a series of the form sum_n ar^nnarn. If |r| < 1|r|<1, then we have sum_(n=0)^ooar^n = a/(1-r)n=0arn=a1r
Both of the series in question are geometric series.

a. sum_(n=0)^oo 0.4^n = 1/(1-0.4) = 5/3n=00.4n=110.4=53

b. sum_(n=1)^oo(-0.1)^n/3 = -1/3 + sum_(n=0)^oo(-0.1)^n/3n=1(0.1)n3=13+n=0(0.1)n3

=-1/3+1/3sum_(n=0)^oo(-0.1)^n=13+13n=0(0.1)n

=-1/3 + 1/3*1/(1-(-0.1))=13+1311(0.1)

=-1/3 + 1/3*10/11=13+131011

=-1/33=133