#### Answer

The next three terms are -7, -6, and -15.

#### Work Step by Step

18, 9, 10, 1, 2,...
To get from 18 to 9, you subtract 9.
To get from 9 to 10, you add 1.
To get from 10 to 1, you subtract 9.
To get from 1 to 2, you add 1.
The pattern is subtract 9, add 1, subtract 9, add 1, and so on, so:
2-9=-7
-7+1=-6
-6-9=-15