How would I write this arith.sequence in standard form?
9,12,15,18

Question

How would I write this arith.sequence in standard form?
9,12,15,18

anonymous · Answer

The common difference is 3. (12-9 or 18-15).

The first term is 9.

So the general term is  a+ (n-1)d

where a = first term
d = common difference.

So in your example, the general term is

9 + (n-1)(3)
= 9 + 3n - 3

= 3n + 6.

anonymous · Answer

Oh, how simple. Thank you.

anonymous · Answer

Welcome. Worth to jot down that general term "formula" for an arithmetic sequence.

anonymous · Answer

One final note...if you have the general term, say 3n+6, as in our last example, you can easily figure out "what would be the 120th term of that sequence". Since you have the general form for the sequence, just substitute n = 120, and you get 3(120) + 6 = 366.

anonymous · Answer

@Yondaime

anonymous · Answer

Wow, that is mighty useful to know. Thank you again!!

anonymous · Answer

Very welcome.