Which expression can be used to determine the nth term in the pattern below?

21, 30, 39, 48, 57, ...

Question

Which expression can be used to determine the nth term in the pattern below?

21, 30, 39, 48, 57, ...

_michaeld22 · Answer

30-21 = 9.
39 - 30 = 9. 
It seems like you're adding 9 each time.. Soo, 57+9 = ?

anonymous · Answer

add 9 4 times

solomonzelman · Answer

$\Large\color{black}{ \bf    a_n=a_{n-1}+9   }$

uri · Answer

There is always a formula for questions like these @_Michaeld22 No use of teaching them directly. :)

_michaeld22 · Answer

Touche.. Lol I don't remember the formulas tho, I just try to help the best I can, and get people like @SolomonZelman to type them for me (:

solomonzelman · Answer

Yeah, I am not in the mood of teaching recursive formulas for this type of sequences. I assume that people have a proper background to the problem they are doing. And if they don't, I apologize for the inconvenience, and leave the question.