(1) 3a = 2(1-2(2+a))+1 ∴ a = -5/7 , S = 9/7
(2) 3(S'-S) = S (1-2S') + 1 , (3+2S)S' = 4S +1, S' = (4S+1) / (2S+3)
(3) f(g(x)) = 4(x+1)+(βx+1) / 2(x+1)+3(βx+1), g(γx) = γx+1 / βγx+1
4+β = 5γ , 2+3β = 5βγ ∴ β=-2, γ= 2/5
(4) S' = T'+1 / -2T'+1 また、 S'= f(S) = f(g(T)) = 2T+5 / -4T+5
二式を連立させて T' = 2/5 T(等比数列)、初項は 1/5
(5) a' = S' - S = 2T+5 / -4T+5 - T+1 / -2T+1 = -9T / (-4T+5)(-2T+1)
T' = 2/5 T ∴ n→∞ならT→0, a'/T → -9 / 5 * 5/2 = -9/2