Diketahui =U3=16 U9=1024 Ditanya =S5?

U3 = a + 2b = 16
u9 = a +8b = 1024

-6b = -1008
b = 168

a = 16 - 168.2
a =-320

u5 = -320 + 168 (4)
u5 = 352

maka S5 = 5/2 (a + u5)
5/2 x (-320 + 352)
5/2 x 32
S5 = 80