Question

Which of the following sequences is not arithmetic?

1, 2, 3, 4, ...
2, 4, 6, 8, ...
0, -2, -4, -6, ...
1, 4, 9, 16, ...

Answer 1

We can find out by checking each one, one at a time:

(A) 2-1=1; 3-2=1, 4-3=1
Same difference each time, so (A) IS arithmetic.

(B) 4-2=2; 6-4=2; 8-6=2
Same difference each time, so (B) IS arithmetic.

(C) -2-0=-2; -4-(-2)=-2; -6-(-4)=-2
Same difference each time, so (C) IS arithmetic.

(D) 4-1=3; 9-4=5; 16=9=7
NOT the same difference each time, so (D) IS NOT arithmetic.