APPENDIX B - Coordinate Geometry and Lines - B Exercises - Page A 16: 51

The region includes all the points that are above the line $y = 1+x$ and below the line $y = 1-2x$ Note that the points on these two lines are also included in the region.

$\{(x,y)\vert~1+x \leq y \leq 1-2x ~\}$ The region includes all the points that are above the line $y = 1+x$ and below the line $y = 1-2x$ Note that the points on these two lines are also included in the region.