Shading half of the plane to show the solution set.
Here, we need to do this process for each of the inequalities in the system.
x<4 & (I) y>1 & (II) y≥- x+1 & (III)
The system's solution set will be the intersection of the shaded regions in the graphs of (I), (III), and (III).
Boundary Lines
We can tell a lot of information about the boundary lines from the inequalities given in the system.
Exchanging the inequality symbols for equals signs gives us the boundary line equations.
Observing the inequality symbols tells us whether the inequalities are strict.
Let's find each of these key pieces of information for the inequalities in the system. Since Inequality (I) is in the form x<4, the slope of its boundary line will be undefined. This boundary line will be vertical. On the other hand, Inequality (II) is in the form y>1. Therefore, the slope of its boundary line will be equal to 0. This boundary line will be horizontal.
Information
Inequality (I)
Inequality (II)
Inequality (III)
Given Inequality
x <4
y > 1
y ≥ - x+1
Boundary Line Equation
x =4
y =1
y =- x+1
Solid or Dashed?
< ⇒ Dashed
> ⇒ Dashed
≥ ⇒ Solid
y= mx+ b
x=4
y= 0x+ 1
y= -1x+ 1
Great! With all of this information, we can plot the boundary lines.
Shading the Solution Sets
Before we can shade the solution set for each inequality, we need to determine on which side of the plane their solution sets lie. To do that, we will need a test point that does not lie on either boundary line.
It looks like the point ( 0, 0) would be a good test point. We will substitute this point for x and y in the given inequalities and simplify. If the substitution creates a true statement, we shade the same region as the test point. Otherwise, we shade the opposite region.
Information
Inequality (I)
Inequality (II)
Inequality (III)
Given Inequality
x<4
y>1
y≥- x+1
Substitute (0,0)
( 0)? <4
( 0)? >1
( 0)? ≥ -( 0)+1
Simplify
0<4 âś“
0≯1 *
0≱1 *
Shaded Region
same
opposite
opposite
For Inequality (I), we will shade the region containing our test point, or to the left of the boundary line. For inequalities (II) and (III), however, we will shade the region opposite the test point, or above the boundary lines.
Finally, to illustrate the solution set, we will only show the overlapping region.
