jika diketahui barisan geometri dengan r= 1/4 dan U^8 = 1/1.024,maka U^4- 2U^5= a.1/2 b.1/4 c.1/6 d.1/8

U8 = ar^7
1/1024 = a x (¼)^7
1/(2^10) = a x ½^14
a = ½^10 ÷ ½^14
a = ½^(10-14) = ½-⁴

U4 - 2U^5
= (½-⁴ x ¼³) - 2(½-⁴ x ¼⁴)
= (4² x 4^-3) - 2(4² x 4^-4)
= ¼ - 2/16
= (4-2)/16
= ⅛