1. jika (a+2), (a-1), (a-7)..... membentuk barisan geometri, tentukan rasionya! 2. jumlah bilangan ganjil 3 + 5 + 7 + .... + k = 440. Tentukan nilai K!

jawab

deret geometri

u1. u3 = u2^2
(a + 2)( a-  7)= (a - 1)²
a²- 5a -14 = a²- 2a + 1
-5a + 2a = 1+ 14
-3a = 15
a = - 5

r = (a - 1)/(a+2)
r = (-5-1)/(-5+2)
r = (-6)/(-3)
r = 2