Question

Find the tenth term of the sequence.
3, 2, -1, -6, -13,...
The tenth term is ?

Answer 1

-78

Explanation:

Odd differences:

3 - 1 = 2

2 - 3 = -1

-1 - 5 = -6

-6 - 7 = -13

-13 - 9 = -22

-22 - 11 = -33

-33 - 13 = -46

-46 - 15 = -61

-61 - 17 = -78

Answer 2

-78

Explanation:

We subtract 1, then 3, then 5, then 7

Then subtract 9,11,13,15,17

-21 -11 = -33

-33 -13 = -46

-46 -15 = -61

-61 -17 = -78

3, 2, -1, -6, -13, -22, -33, -46, -61, -78