diketahui barisan arimatika: 3,12,21 carilah n, jika Un= 237

Un = a+(n-1)b
237 = 3+(n-1)9
237-3 = 9n-9
234 = 9n-9
234+9 = 9n
243 = 9n
243/9 = n
27 = n

3,13,21
B= U2-U1= 12-3=9
Un= a+(n-1)b
U237 = 3+(237-1)9
= 3+(236)9
= 3+ 2.124
= 2.127