Jika dari suatu barisan geometri diketahui Un=12 dan Un+3=96 maka Un+4 adalah

Un = 12 = ar^(n-1)

      12 = ar^(n) / r

      12r = ar^(n)

U₍ₙ₊₃₎ = 96 = ar^(n+3 –  1) = ar^(n+2)

U₍ₙ₊₄₎ = ar^(n+3) = ?

U₍ₙ₊₄₎ = ar^(n+3) = ar^(n+2) . r <=ar^(n+3) = 96

                        = 96r = 8. 12r

Un + U(n+3) = 12+96

ar^(n-1)+ar^(n+2) = 108

ar^(n)(r^(-1)+r^(2)) = 108

12r(r^(-1)+r^(2)) = 108

12+12r² = 108

12r² = 96

r² = 8

r = 2√2

12r = 24√2

U(n+4) = 8.12r = 8.(24√2)

                       = 192√2