Suku ke 80 barisan bilangan 15,24,35,48,.....adalah

jawab

15, 24, 35, 48
....9...11...13
.......2....2
a= 15
b = 9
c = 2
un = a +(n-1)b + 1/2 c (n-1)(n-2)

u80 = 15 +(80-1)9 + (80-1)(80-2)
u80 = 15 +711 + 6.162
u80= 6,888