tentukan rasio,rumus suku ke:n dan suku ke:10 dari barisan geometri berikut: a) 1,4,16,64,… b) 3,-6,12,-24…. c) 4+2+1+½+….

A) 1,4,16,64,…
r = 4/1 = 4
Un = 1 x 4ⁿ-¹
U10 = 1 x 4^(10-1) = 4^9 = 262.144

b) 3,-6,12,-24….
r = -6/3 = -2
Un = 3 x (-2)ⁿ-¹
U10 = 3 x (-2)^(10-1) = 3 x (-2)^9 = 3 x (-512) = -1.536

c) 4+2+1+½+….
r = 2/4 = ½
Un = 4 x ½ⁿ-¹
Un = 2² x 2¹-ⁿ
Un = 2³-ⁿ
U10 = 2^(3-10) = 2^-7 = (½)^7 = 1/128