We have the following equations:
![(1) \ y=-0.5x+5 \\ (2) \ y=-1.25x+8](https://tex.z-dn.net/?f=%281%29%20%5C%20y%3D-0.5x%2B5%20%5C%5C%20%282%29%20%5C%20y%3D-1.25x%2B8)
So we are asked to write a system of equations or inequalities for each region and each point.
Part a)Region Example A
Region B.
Let's take a point that is in this region, that is:
![P(0,6)](https://tex.z-dn.net/?f=P%280%2C6%29)
So let's find out the signs of each inequality by substituting this point in them:
![y \ (?)-0.5x+5 \\ 6 \ (?) -0.5(0)+5 \\ 6 \ (?) \ 5 \\ 6\ \textgreater \ 5 \\ \\ y \ (?) \ -1.25x+8 \\ 6 \ (?) -1.25(0)+8 \\ 6 \ (?) \ 8 \\ 6\ \textless \ 8](https://tex.z-dn.net/?f=y%20%5C%20%28%3F%29-0.5x%2B5%20%20%5C%5C%206%20%5C%20%28%3F%29%20-0.5%280%29%2B5%20%5C%5C%206%20%5C%20%28%3F%29%20%5C%205%20%5C%5C%206%5C%20%5Ctextgreater%20%5C%205%20%5C%5C%20%20%5C%5C%20y%20%5C%20%28%3F%29%20%5C%20-1.25x%2B8%20%5C%5C%206%20%5C%20%28%3F%29%20-1.25%280%29%2B8%20%5C%5C%206%20%5C%20%28%3F%29%20%5C%208%20%5C%5C%206%5C%20%5Ctextless%20%5C%208)
So the inequalities are:
Region C.
A point in this region is:
![P(0,10)](https://tex.z-dn.net/?f=P%280%2C10%29)
So let's find out the signs of each inequality by substituting this point in them:
![y \ (?)-0.5x+5 \\ 10 \ (?) -0.5(0)+5 \\ 10 \ (?) \ 5 \\ 10\ \textgreater \ 5 \\ \\ y \ (?) \ -1.25x+8 \\ 10 \ (?) -1.25(0)+8 \\ 10 \ (?) \ 8 \\ 10 \ \ \textgreater \ \ 8](https://tex.z-dn.net/?f=y%20%5C%20%28%3F%29-0.5x%2B5%20%5C%5C%2010%20%5C%20%28%3F%29%20-0.5%280%29%2B5%20%5C%5C%2010%20%5C%20%28%3F%29%20%5C%205%20%5C%5C%2010%5C%20%5Ctextgreater%20%5C%205%20%5C%5C%20%5C%5C%20y%20%5C%20%28%3F%29%20%5C%20-1.25x%2B8%20%5C%5C%2010%20%5C%20%28%3F%29%20-1.25%280%29%2B8%20%5C%5C%2010%20%5C%20%28%3F%29%20%5C%208%20%5C%5C%2010%20%5C%20%5C%20%5Ctextgreater%20%5C%20%20%5C%208)
So the inequalities are:
Region D.
A point in this region is:
![P(8,0)](https://tex.z-dn.net/?f=P%288%2C0%29)
So let's find out the signs of each inequality by substituting this point in them:
![y \ (?)-0.5x+5 \\ 0 \ (?) -0.5(8)+5 \\ 0 \ (?) \ 1 \\ 0 \ \ \textless \ \ 1 \\ \\ y \ (?) \ -1.25x+8 \\ 0 \ (?) -1.25(8)+8 \\ 0 \ (?) \ -2 \\ 0 \ \ \textgreater \ \ -2](https://tex.z-dn.net/?f=y%20%5C%20%28%3F%29-0.5x%2B5%20%5C%5C%200%20%5C%20%28%3F%29%20-0.5%288%29%2B5%20%5C%5C%200%20%5C%20%28%3F%29%20%5C%201%20%5C%5C%200%20%5C%20%5C%20%5Ctextless%20%5C%20%20%5C%201%20%5C%5C%20%5C%5C%20y%20%5C%20%28%3F%29%20%5C%20-1.25x%2B8%20%5C%5C%200%20%5C%20%28%3F%29%20-1.25%288%29%2B8%20%5C%5C%200%20%5C%20%28%3F%29%20%5C%20-2%20%5C%5C%200%20%5C%20%5C%20%5Ctextgreater%20%5C%20%5C%20-2)
So the inequalities are:
Point P:This point is the intersection of the two lines. So let's solve the system of equations:
![(1) \ y=-0.5x+5 \\ (2) \ y=-1.25x+8 \\ \\ Subtracting \ these \ equations: \\ 0=0.75x-3 \\ \\ Solving \ for \ x: \\ x=4 \\ \\ Solving \ for \ y: \\ y=-0.5(4)+5=3](https://tex.z-dn.net/?f=%281%29%20%5C%20y%3D-0.5x%2B5%20%5C%5C%20%282%29%20%5C%20y%3D-1.25x%2B8%20%5C%5C%20%5C%5C%20Subtracting%20%5C%20these%20%5C%20equations%3A%20%5C%5C%200%3D0.75x-3%20%5C%5C%20%5C%5C%20Solving%20%5C%20for%20%5C%20x%3A%20%5C%5C%20x%3D4%20%5C%5C%20%20%5C%5C%20Solving%20%5C%20for%20%5C%20y%3A%20%5C%5C%20y%3D-0.5%284%29%2B5%3D3%20)
Accordingly, the point is:
Point q:
This point is the
![x-intercept](https://tex.z-dn.net/?f=x-intercept)
of the line:
![y=-0.5x+5](https://tex.z-dn.net/?f=y%3D-0.5x%2B5)
So let:
![y=0](https://tex.z-dn.net/?f=y%3D0%20)
Then
![x=\frac{5}{0.5}=10](https://tex.z-dn.net/?f=x%3D%5Cfrac%7B5%7D%7B0.5%7D%3D10)
Therefore, the point is:
![\boxed{q(10,0)}](https://tex.z-dn.net/?f=%5Cboxed%7Bq%2810%2C0%29%7D)
Part b)
The coordinate of a point within a region must satisfy the corresponding system of inequalities. For each region we have taken a point to build up our inequalities. Now we will take other points and prove that these are the correct regions.
Region Example A
The origin is part of this region, therefore let's take the point:
![O(0,0)](https://tex.z-dn.net/?f=O%280%2C0%29)
Substituting in the inequalities:
![y \leq -0.5x+5 \\ 0 \leq -0.5(0)+5 \\ \boxed{0 \leq 5} \\ \\ y \leq -1.25x+8 \\ 0 \leq -1.25(0)+8 \\ \boxed{0 \leq 8}](https://tex.z-dn.net/?f=y%20%5Cleq%20-0.5x%2B5%20%5C%5C%200%20%5Cleq%20-0.5%280%29%2B5%20%5C%5C%20%5Cboxed%7B0%20%5Cleq%205%7D%20%5C%5C%20%5C%5C%20y%20%5Cleq%20-1.25x%2B8%20%5C%5C%200%20%5Cleq%20-1.25%280%29%2B8%20%5C%5C%20%5Cboxed%7B0%20%5Cleq%208%7D)
It is
true.
Region B.
Let's take a point that is in this region, that is:
![P(0,7)](https://tex.z-dn.net/?f=P%280%2C7%29)
Substituting in the inequalities:
![y \geq -0.5x+5 \\ 7 \geq -0.5(0)+5 \\ \boxed{7 \geq \ 5} \\ \\ y \leq \ -1.25x+8 \\ 7 \ \leq -1.25(0)+8 \\ \boxed{7 \leq \ 8}](https://tex.z-dn.net/?f=y%20%5Cgeq%20-0.5x%2B5%20%5C%5C%207%20%5Cgeq%20-0.5%280%29%2B5%20%5C%5C%20%5Cboxed%7B7%20%5Cgeq%20%5C%205%7D%20%5C%5C%20%5C%5C%20y%20%20%5Cleq%20%5C%20-1.25x%2B8%20%5C%5C%207%20%5C%20%5Cleq%20-1.25%280%29%2B8%20%5C%5C%20%5Cboxed%7B7%20%5Cleq%20%5C%208%7D)
It is
true
Region C.
Let's take a point that is in this region, that is:
![P(0,11)](https://tex.z-dn.net/?f=P%280%2C11%29)
Substituting in the inequalities:
![y \geq -0.5x+5 \\ 11 \geq -0.5(0)+5 \\ \boxed{11 \geq \ 5} \\ \\ y \geq \ -1.25x+8 \\ 11 \ \geq -1.25(0)+8 \\ \boxed{11 \geq \ 8}](https://tex.z-dn.net/?f=y%20%5Cgeq%20-0.5x%2B5%20%5C%5C%2011%20%5Cgeq%20-0.5%280%29%2B5%20%5C%5C%20%5Cboxed%7B11%20%5Cgeq%20%5C%205%7D%20%5C%5C%20%5C%5C%20y%20%5Cgeq%20%5C%20-1.25x%2B8%20%5C%5C%2011%20%5C%20%5Cgeq%20-1.25%280%29%2B8%20%5C%5C%20%5Cboxed%7B11%20%5Cgeq%20%5C%208%7D)
It is
true
Region D.
Let's take a point that is in this region, that is:
![P(9,0)](https://tex.z-dn.net/?f=P%289%2C0%29)
Substituting in the inequalities:
![y \leq -0.5x+5 \\ 0 \leq -0.5(9)+5 \\ \boxed{0 \leq \ 0.5} \\ \\ y \geq \ -1.25x+8 \\ 0 \geq -1.25(9)+8 \\ \boxed{0 \geq \ -3.25}](https://tex.z-dn.net/?f=y%20%20%5Cleq%20-0.5x%2B5%20%5C%5C%200%20%5Cleq%20-0.5%289%29%2B5%20%5C%5C%20%5Cboxed%7B0%20%5Cleq%20%5C%200.5%7D%20%5C%5C%20%5C%5C%20y%20%5Cgeq%20%5C%20-1.25x%2B8%20%5C%5C%200%20%5Cgeq%20-1.25%289%29%2B8%20%5C%5C%20%5Cboxed%7B0%20%5Cgeq%20%5C%20-3.25%7D)
It is
true