Jawabanmu

2014-02-27T13:24:05+07:00
S2=72 S4=80 U10=...? S4:S2 = a (r^4-1)/r-1 : a (r^2-1)/r-1 = 80/72 a (r^4-1)/r-1 x r-1/a (r^2-1) = 5/4 (r^4-1)/(r^2-1) = 5/4 (r^2-1) (r^2+1)/(r^2-1) = 5/4 (r^2+1) = 5/4 r^2 = 5/4 - 1 r^2 = 1/4 r = 1/2 S2 = a + a.r = 72 a + a.1/2 = 72 3/2 a = 72 a = 72 x 2/3 a = 48 U10 = ar^9 U10 = 48 x (1/2)^9 U10 = 48 x 1/512 U10 = 48/512 U10 = 3/32