Find the next three terms in the sequence

3, 12, 21, 30, . . .

4 answers

looks to me as the sequence is to add 9 to the last number...
Does anyone have all the answers
12 - 3 = 9

21 - 12 = 9

31 - 21 = 9

The common difference of successive members is 9

This is arithmetic progression.

In arithmetic progression:

an = a1 + ( n - 1 ) * d

In this case:

a1 = 3 , d = 9

an = a1 + ( n - 1 ) * d

an = 3 + ( n - 1 ) * 9

an = 3 + 9 n - 9

an = 9 n - 6

n = 1

a1 = 9 * 1 - 6 = 9 - 6 = 3

n = 2

a2 = 9 * 2 - 6 = 18 - 6 = 12

n = 3

a3 = 9 * 3 - 6 = 27 - 6 = 21

n = 4

a4 = 9 * 4 - 6 = 36 - 6 = 30

n = 5

a5 = 9 * 5 - 6 = 35 - 6 = 39

n = 6

a1 = 9 * 6 - 6 = 56 - 6 = 48

n = 7

a1 = 9 * 7 - 6 = 63 - 6 = 57

The next three terms:

39 , 48 , 57
3,12,21,30,...if an = 201