Posted by leo on .
Which is an arithmetic sequence?
A. 1, 4, 9, 16, . . .
B. 2, 1, –1, –4, . . .
C. 4, 8, 16, 32, . . .
D. 21, 9, –3, –15, . . .
.
help please

algebrall 
Steve,
an arithmetic sequence has a constant difference between terms. Looking at the differences, we see:
A. 3,5,7, . . .
B. 1,2,3, . . .
C. 4,8,16, . . .
D. 12,12,12, . . .
I guess the answer is D, eh?