Consider the infinite geometric sequence 25 , 5 , 1 , 0.2 , ... (a) Find the common ratio. (b) Find (i) the 10th term; (ii) an expression for the nth term. (c) Find the sum of the infinite sequence.
QUESTION (a) R = U(n+1)/U(n ) = 5/25= 0.2(b) (i) U(10) = 25 x (1/5)^9 = 0.0000128 (ii) U(n) = 25 x (1/5)^(n-1)(c) S = U(1)/(1-r) = 25/(1-(1/5))=25/(4/5))=125/4=31.25
