jika a+1,a-1,a-5 membentuk deretgeometri tentukan nilai a

Deret geometri

U2/U1 = U3/U2

(a-1)/ (a+1) = (a-5)/(a-1)

(a-1) (a-1) = (a-5) (a+1)

a^2 - 2a + 1 = a^2 -4a -5

-2a + 4a = -5 -1

2a = -6

a = -6/2

a = -3