C.Presenting
examples/
instances of
the lesson
The words used in the activity are some of the
“Inequalities” that we use in a real life situation.
Let us study more examples and see its
translation in mathematical sentence.
The underlined words in the example above are
just few of the examples of inequalities that are
evident in a real life situation. These words can
be expressed using mathematical symbol.
A linear inequality in two variables is simply a
linear equation but instead of having an equal
sign (=) it will be replaced by an inequality sign.
The points (2, 7), (0, 3) and (-1, 1) are the points on
the line y = 2x + 3 and the solutions to the given
equation. To determine if it is true, substitute the
coordinates in the equation.
y = 2x + 3:
(2, 7)
x = 2 and y = 7
7 = 2(2) + 3
7 = 4 + 3
7=7 True
y=2x+3;(-1,1)
x=-1 and y=1
1=2(-1)+3
1=(-2)+3
1=1 True
y =2x + 3: (0,3)
x=0 and y=3
3=2(0)+3
3=0+3
3=3 True
Likewise, in determining if a point is a solution to
the linear inequality in two variables, substitute
the coordinates to the inequality and apply the
Law of Trichotomy.
Example: Determine if the points (5, 8), (0, 0), and
(10, 10) are solutions to the linear inequality
2x + 5y > 10.
2x + 5y ≥ 10;(5,0)
x = 5 and y = 0
2(5) + 5(0) ≥ 10
10 + 0 ≥ 10
10 ≥ 10 False
Thus, (0, 0) is a solution to 2x + 5y > 10
Let us now try to replace “=” to ≥, so it becomes
y ≥ 2x + 3. We can notice that the points on the
line are still part of the solution therefore we will
still use a solid line. Points (-6, -2), (-3, 3), (-2, 0),
(1, 7), and (-5, -4) are also solutions to the
inequality y ≥ 2x + 3. Observe the example
below:
The graph of the inequality y ≥ 2x + 3 is half of
the plane. It means that all the points on the left
side of the line is part of the solution and as well
as the points on the line.
Let us now try to replace “=” to ≥, so it becomes
y ≥ 2x + 3. We can notice that the points on the
line are still part of the solution therefore we will
still use a solid line. Points (-6, -2), (-3, 3), (-2, 0),
(1, 7), and (-5, -4) are also solutions to the
inequality y ≥ 2x + 3. Observe the example