suku ke 14 barisan 15,24,35,48,63.

MAPEL = MATEMATIKA
KELAS = 9
BAB = BARISAN & DERET

diketahui suatu barisan :
15, 24, 35, 48, 63
....9,...11,...13,..15,....
.......2,...2,...2,........

a = 15
b1 = 9
b2 = 2

ditanya = U14 ??

----------- Barisan Aritmatika --------

U14 = a + ( n-1 )(b1) + ( n-1 )( n-2 )(b2)/(2)
U14 = 15 + ( 14-1 )(9) + ( 14-1 )( 14-2 )(2)/(2)
U14 = 15 + (13)(9) + (13)(12)/(1)
U14 = 15 + 117 + 156
U14 = 288

jadi suku ke-14 = 288
semoga membantu