tolong donk sama caranya plisss...

U1 = (a+2) = x
U2 = (a-1) = x*r
U3 = (a-7) = x*r²

r = r
U2/U1 = U3/U2
(a-1) / (a+2) = (a-7) / (a-1)
(a-1)(a-1) = (a-7)(a+2)
a² - 2a + 1 = a² - 5a - 14
3a = -15
a = -5

U1 = x = a+2 = -5 + 2 = -3
U2 = x*r = a-1 = -5 - 1 = -6

r = U2/U1 = -6/-3 = 2

semoga bermanfaat