Suku keberapakah 117 dari barisan aritmetika : 7,12,17,22,....???

7,12,17,22,27,32,37,42,47,52,57,62,67,72,77,82,87,92,97,102,107,117,122
117 ke 23

Un= a + (n-1) b

a= 7
b= U2-U1
= 12-7
= 5
jawab:
U117= a + (n-1) b
= 7 + (117-1) 5
= 7 + 580
= 587
atau
a= 7 b= 5
7-5= 2
jadi
U117 =5n + 2 = 5.117 + 2
= 587