Back to homeMathematics · Integrated Math III · Change subject
Start for free
Math III · Mathematics
Equations · Inequalities and systems of inequalities

Systems of Linear Inequalities in Two Variables

Maya is baking for the school bake sale. A batch of cookies uses 2 cups of flour and 1 cup of sugar. A batch of brownies uses 3 cups of flour and 1 cup of sugar. She has 12 cups of flour and 5 cups of sugar. Can she bake 4 batches of cookies and 2 batches of brownies? And what are all the combinations she could bake?

One inequality with one variable gave you an interval on a number line. With two variables, $x$ and $y$, the answer lives in the coordinate plane: it is a whole region. By the end of this page you will be able to draw that region, find its corners, and answer Maya's question.

One Inequality: A Half-Plane

The boundary line splits the plane in two. Every point on one side makes the inequality true, and every point on the other side makes it false. To find out which side is which, you only need to test one point.

Graph of 2x − y < 4: the half-plane containing the origin is shaded and the boundary line is dashed. The point (0, 0) is inside and (3, 1) is outside. (0, 0) ✓ (3, 1) ✗ 2x − y = 4

Drag the point and read its coordinates. Then substitute them into $2x - y < 4$ to see whether it should land in the shaded region of the figure above.

Practice★☆☆Not started
Graphically represent the inequality $2x - 3y \le 6$. Then, indicate two points whose coordinates belong to the solution region and two points that do not belong.

Graphically represent the inequality $2x - 3y \le 6$. Then, indicate two points whose coordinates belong to the solution region and two points that do not belong.

Solve

Systems: The Overlap of Half-Planes

To graph a system, graph each inequality on the same axes and keep only the region where the shadings overlap.

Graph of y ≤ −x + 4 with a solid boundary and y > x − 2 with a dashed boundary. The solution region is the wedge below the first line and above the second, opening to the left. The corner point (3, 1) is not included. (3, 1) y ≤ −x + 4 y > x − 2
Practice★☆☆Not started
Given the system of linear inequalities $x + y < 5$ and $2x - y \ge 0$, determine which of the following points are solutions to the system: $A(2, 1)$, $B(0, 0)$,…

Given the system of linear inequalities $x + y < 5$ and $2x - y \ge 0$, determine which of the following points are solutions to the system: $A(2, 1)$, $B(0, 0)$, $C(3, 3)$ and $D(4, 0)$.

Solve
Practice★☆☆Not started
Graphically represent the system formed by the inequalities $x + 2y \ge 4$ and $x - y \le 1$, clearly shading the resulting feasible region.

Graphically represent the system formed by the inequalities $x + 2y \ge 4$ and $x - y \le 1$, clearly shading the resulting feasible region.

Solve
Practice★☆☆Not started
Check algebraically if the point $P(1, 2)$ belongs to the region defined by the system of inequalities: $2x + y \le 5$, $x - 3y \ge -6$ and $3x + 2y \ge 1$.

Check algebraically if the point $P(1, 2)$ belongs to the region defined by the system of inequalities: $2x + y \le 5$, $x - 3y \ge -6$ and $3x + 2y \ge 1$.

Solve

Vertices of the Feasible Region

When the overlap is a closed polygon, it is called the feasible region. Its corners, the vertices, are the points that matter most in applications such as linear programming (finding the best production plan).

Feasible region of x ≥ 0, y ≥ 0, x + 2y ≤ 8 and 3x + y ≤ 9: a quadrilateral with vertices (0, 0), (3, 0), (2, 3) and (0, 4). (0, 0) (3, 0) (2, 3) (0, 4)
Practice★☆☆Not started
Find algebraically the coordinates of the vertices of the feasible region defined by the following system of inequalities: $x \ge 0$, $y \ge 0$ and $x + y \le 4$.

Find algebraically the coordinates of the vertices of the feasible region defined by the following system of inequalities: $x \ge 0$, $y \ge 0$ and $x + y \le 4$.

Solve
Practice★★☆Not started
Graphically represent the system of inequalities $\frac{x}{2} + \frac{y}{3} \le 1$, $x - \frac{y}{2} \ge -1$ and $y \ge 0$. Calculate the exact coordinates of the…

Graphically represent the system of inequalities $\frac{x}{2} + \frac{y}{3} \le 1$, $x - \frac{y}{2} \ge -1$ and $y \ge 0$. Calculate the exact coordinates of the vertices of the resulting region.

Solve
Practice★★☆Not started
Calculate the area of the region of the plane defined by the following system of inequalities: $y \le x + 2$, $y \ge -x + 2$ and $y \le 4$.

Calculate the area of the region of the plane defined by the following system of inequalities: $y \le x + 2$, $y \ge -x + 2$ and $y \le 4$.

Solve

Writing a System from a Graph

Sometimes you are given the picture and must write the inequalities. Do it one side of the region at a time.

Triangular region with vertices (1, 1), (5, 1) and (3, 4), with the interior point (3, 2) marked. (1, 1) (5, 1) (3, 4) (3, 2)
Practice★☆☆Not started
From the shaded region in the figure, determine the linear inequality with two unknowns that defines it. Bear in mind that the boundary line passes through the points…

From the shaded region in the figure, determine the linear inequality with two unknowns that defines it. Bear in mind that the boundary line passes through the points $(0, 2)$ and $(3, 0)$ and that the region includes the origin.

X Y (0, 2) (3, 0)
Solve
Practice★★☆Not started
The figure shows a polygonal region on the Cartesian plane that represents the viable production combinations of two electronic components. Determine the system of…

The figure shows a polygonal region on the Cartesian plane that represents the viable production combinations of two electronic components. Determine the system of inequalities that defines this region, knowing that its vertices are $A(1, 1)$, $B(5, 1)$, $C(4, 4)$ and $D(2, 3)$.

A B C D X Y
Solve
Practice★★★Not started
The image shows a feasible region in the shape of a quadrilateral, which models the limitations of a software engineering project (programming hours on the $X$-axis vs…

The image shows a feasible region in the shape of a quadrilateral, which models the limitations of a software engineering project (programming hours on the $X$-axis vs testing hours on the $Y$-axis). The vertices are $P(0, 4)$, $Q(2, 5)$, $R(5, 2)$ and $S(3, 0)$. Determine the system of inequalities that exactly defines this region.

P Q R S X Y
Solve

Word Problems: Writing the Constraints

Many real situations have limited resources: hours, ingredients, money, seats. Each limit becomes an inequality, called a constraint.

Words Symbol
at least, no fewer than, a minimum of $\ge$
at most, no more than, cannot exceed, a maximum of $\le$
more than / fewer than $>$ / $<$
between $a$ and $b$ (inclusive) $a \le \text{expr} \le b$, two inequalities
$y$ cannot exceed twice $x$ $y \le 2x$
Feasible region for Maya's bake sale: a quadrilateral with vertices (0, 0), (5, 0), (3, 2) and (0, 4). (0, 0) (5, 0) (3, 2) (0, 4) x: batches of cookies y: batches of brownies
Practice★★☆Not started
A bakery makes two types of cakes, T1 and T2. Cake T1 requires $2$ hours of preparation and $1$ hour of baking, while cake T2 requires $1$ hour of preparation and $2$…

A bakery makes two types of cakes, T1 and T2. Cake T1 requires $2$ hours of preparation and $1$ hour of baking, while cake T2 requires $1$ hour of preparation and $2$ hours of baking. A maximum of $10$ hours of preparation and $8$ hours of baking are available per day. Set up the system of inequalities that models this situation (considering that the quantities cannot be negative) and graphically represent the region of possible daily productions.

Solve
Practice★★☆Not started
A farmer has $50$ acres to plant wheat and barley. Wheat seed costs $\$20$ per acre and barley seed costs $\$30$ per acre. The maximum budget for seeds is $\$1200…

A farmer has $50$ acres to plant wheat and barley. Wheat seed costs $\$20$ per acre and barley seed costs $\$30$ per acre. The maximum budget for seeds is $\$1200$. In addition, due to environmental regulations, the area of barley cannot exceed twice the area of wheat. Write the associated system of inequalities and find the vertices of the feasible region.

Solve
Practice★★☆Not started
A personal trainer plans a routine with strength exercises ($x$) and cardio exercises ($y$). The total training time must be between $40$ and $60$ minutes. Each strength…

A personal trainer plans a routine with strength exercises ($x$) and cardio exercises ($y$). The total training time must be between $40$ and $60$ minutes. Each strength exercise lasts $5$ minutes and each cardio exercise lasts $10$ minutes. In addition, the number of strength exercises must be at least equal to the number of cardio exercises. Set up the system of inequalities and represent it graphically.

Solve

Reading Answers from the Region

Once you have the feasible region, you can answer questions about it: Is this plan allowed? What is the most of one item I can make? Where are the corners?

Feasible region for Chloe's homework plan: a quadrilateral with vertices (3, 2), (4, 2), (8, 4) and (3, 9), cut by the vertical segment x = 5 from y = 2.5 to y = 7. (3, 2) (4, 2) (8, 4) (3, 9) x = 5 x: math hours y: science hours
Practice★★☆Not started
To transport $60$ tons of goods, a logistics company has large trucks with a capacity of $8$ tons and small trucks with a capacity of $5$ tons. Due to staffing…

To transport $60$ tons of goods, a logistics company has large trucks with a capacity of $8$ tons and small trucks with a capacity of $5$ tons. Due to staffing restrictions, no more than $10$ vehicles can be sent in total. Set up the system of inequalities that determines the number of trucks of each type that can be used and find algebraically the vertices of the solution region.

Solve
Practice★★★Not started
For the organization of a concert, VIP tickets ($x$) and standard tickets ($y$) are sold. The maximum capacity of the venue is $5000$ people. For safety and…

For the organization of a concert, VIP tickets ($x$) and standard tickets ($y$) are sold. The maximum capacity of the venue is $5000$ people. For safety and profitability reasons, the number of standard tickets cannot exceed three times the number of VIP tickets. In addition, the organizers require that at least $1000$ VIP tickets are sold. Write the system of inequalities, find the vertices of the feasible region and determine algebraically if it is possible to sell exactly $1500$ VIP tickets and $4000$ standard tickets.

Solve
Practice★★★Not started
A furniture factory produces chairs and tables. Each chair requires $2$ hours of cutting and $1$ hour of assembly. Each table requires $1$ hour of cutting and $3$ hours…

A furniture factory produces chairs and tables. Each chair requires $2$ hours of cutting and $1$ hour of assembly. Each table requires $1$ hour of cutting and $3$ hours of assembly. The workers can dedicate a maximum of $40$ hours per week to cutting and $60$ hours to assembly. In addition, due to a previous contract, at least $5$ tables must be manufactured per week and the number of chairs cannot be less than the number of tables. Set up the system of inequalities, represent it and find all the vertices of the feasible region.

Solve

Unbounded, Empty, and Special Regions

Not every system gives a nice closed polygon.

Unbounded region of x ≥ 0, y ≥ 0 and x + y ≥ 3, which extends up and to the right with two vertices, (3, 0) and (0, 3). (3, 0) (0, 3) keeps going →
Practice★☆☆Not started
Represent the solution set of the system formed by the inequalities $x + y \ge 2$ and $x + y \le 5$. Describe what type of geometric region is obtained.

Represent the solution set of the system formed by the inequalities $x + y \ge 2$ and $x + y \le 5$. Describe what type of geometric region is obtained.

Solve
Practice★★★Not started
Consider the region of the plane defined by the inequalities $x + 2y \ge 4$, $3x - y \le 6$ and $x - y \ge -2$. Prove algebraically that it is an unbounded region and…

Consider the region of the plane defined by the inequalities $x + 2y \ge 4$, $3x - y \le 6$ and $x - y \ge -2$. Prove algebraically that it is an unbounded region and determine the coordinates of the only vertex that this region has.

Solve
Practice★★★Not started
A nutritionist designs a diet based on two foods, X and Y. Each portion of food X provides $20$ oz of protein, $10$ oz of fat and $40$ oz of carbohydrates. Each portion…

A nutritionist designs a diet based on two foods, X and Y. Each portion of food X provides $20$ oz of protein, $10$ oz of fat and $40$ oz of carbohydrates. Each portion of Y provides $15$ oz of protein, $20$ oz of fat and $30$ oz of carbohydrates. The diet must provide at least $120$ oz of protein, no more than $100$ oz of fat and exactly $240$ oz of carbohydrates. Set up the associated system of inequalities and equations. Is it a two-dimensional region or a line segment? Justify your answer and find the endpoints of the solution set.

Solve

Summary

See all the exercises in this section