Back to homeMathematics · 4th ESO B · Change subject
Start for free
ESO Y4B · Mathematics
Equations and systems · Equations, inequalities and systems

Inequalities with two unknowns

The solution of an inequality with two unknowns is not a line but a whole half-plane: one of the two sides into which a line divides the plane. This idea is the basis of linear programming, which companies and factories use to share out resources in the most profitable way.

Before you start, make sure you know: Linear and affine functions (3rd ESO)
Before you start, make sure you know: Systems of equations (3rd ESO)

The line divides the plane into two half-planes

Solution half-plane of the linear inequality x + 2y › 4 with the boundary line and test points checked. x + 2y > 4 yes no
Practice★☆☆Not started
Check which of the following points are solutions to the inequality $3x - 2y \le 6$: $A(0, 0)$ $B(4, 1)$ $C(2, -1)$ $D(-2, -5)$

Check which of the following points are solutions to the inequality $3x - 2y \le 6$:

  • $A(0, 0)$

  • $B(4, 1)$

  • $C(2, -1)$

  • $D(-2, -5)$

Solve
Practice★☆☆Not started
Given the inequality $4x - 5y < 20$, state with reasoning whether the points lying exactly on the line $4x - 5y = 20$ form part of the solution region.

Given the inequality $4x - 5y < 20$, state with reasoning whether the points lying exactly on the line $4x - 5y = 20$ form part of the solution region.

Solve

From the graph to the inequality, and back

Shaded region in the first quadrant bounded by the coordinate axes and the solid line x + y = 4. 4 4

To read a region from a graph, first identify its boundary lines: where they cross the axes, whether they are solid or dashed, and which side is shaded. Each line gives an inequality; the set of inequalities describes the whole region.

Practice★☆☆Not started
Write the linear inequality in two unknowns whose solution region is represented in the following graph. Pay attention to whether the boundary line is solid or dashed.

Write the linear inequality in two unknowns whose solution region is represented in the following graph. Pay attention to whether the boundary line is solid or dashed.

X Y
Solve
Practice★☆☆Not started
Graphically represent the solution region of the inequality $x + 2y > 4$ on the Cartesian plane. You can do it on paper and send a photo with your answer.

Graphically represent the solution region of the inequality $x + 2y > 4$ on the Cartesian plane.

You can do it on paper and send a photo with your answer.

Solve
Practice★★☆Not started
Find the system of inequalities that defines the shaded region in the following graph:

Find the system of inequalities that defines the shaded region in the following graph:

X Y 4 4
Solve

Systems: the feasible region

Triangular feasible region bounded by three lines, showing their vertices. vertices = corners of the region
Practice★☆☆Not started
Determine whether the points $P(1, 3)$, $Q(-1, 2)$ and $R(4, 0)$ belong to the feasible region defined by the following system of inequalities: $x + y \le 5$…

Determine whether the points $P(1, 3)$, $Q(-1, 2)$ and $R(4, 0)$ belong to the feasible region defined by the following system of inequalities:

$x + y \le 5$

$2x - y > -1$

Solve
Practice★☆☆Not started
Graphically represent the system of inequalities that defines the fourth quadrant of the Cartesian plane (where the x-coordinate is non-negative and the y-coordinate is…

Graphically represent the system of inequalities that defines the fourth quadrant of the Cartesian plane (where the x-coordinate is non-negative and the y-coordinate is non-positive).

You can do it on paper and send a photo with your answer.

Solve
Practice★★☆Not started
Graphically represent the feasible region defined by the following system of inequalities: $2x + y \le 6$ $x - y \ge -1$ $y \ge 0$ You can do it on paper and send a…

Graphically represent the feasible region defined by the following system of inequalities:

$2x + y \le 6$

$x - y \ge -1$

$y \ge 0$

You can do it on paper and send a photo with your answer.

Solve

Linear programming: sharing-out and production problems

Sharing a budget, parts or time between two products leads naturally to a system of inequalities with two unknowns: each constraint (money, hours, units available) is an inequality, and the possible combinations form the feasible region.

Graphical comparison between the intersection of two half-planes, which forms the feasible region, and their incorrect union. 1. Unknownsx, y: quantities 2. Constraintseach piece of data = inequality 3. Regionfeasible, and vertices
Practice★★☆Not started
To organise a party, soft drink bottles are bought at $2$ € each and bags of snacks at $3$ € each. If the maximum budget is $30$ € and at least one unit of each product…

To organise a party, soft drink bottles are bought at $2$ € each and bags of snacks at $3$ € each. If the maximum budget is $30$ € and at least one unit of each product must be bought, set up the corresponding system of inequalities and give two possible valid purchase combinations.

Solve
Practice★★☆Not started
In a test with $20$ questions, each correct answer adds $2$ points and each incorrect answer subtracts $1$ point. If a candidate needs at least $15$ points to pass, set…

In a test with $20$ questions, each correct answer adds $2$ points and each incorrect answer subtracts $1$ point. If a candidate needs at least $15$ points to pass, set up the inequality relating the number of correct answers ($x$) and the number of incorrect answers ($y$). Given that $x \ge 0$, $y \ge 0$ and $x+y \le 20$, graphically represent the region of possible combinations to pass.

You can do it on paper and send a photo with your answer.

Solve
Practice★★☆Not started
A workshop manufactures bicycles and tricycles. Each bicycle requires $2$ wheels and each tricycle $3$ wheels. There are $60$ wheels left in the warehouse. Furthermore,…

A workshop manufactures bicycles and tricycles. Each bicycle requires $2$ wheels and each tricycle $3$ wheels. There are $60$ wheels left in the warehouse. Furthermore, it is known that the number of bicycles manufactured must be at least double the number of tricycles. Set up the system of inequalities that models this situation.

Solve

Quadratic inequalities with two unknowns

When the boundary is not a line but a parabola, the reasoning is the same: the curve $y=ax^2+bx+c$ divides the plane into two regions, "above" ($y>\ldots$) and "below" ($y<\ldots$).

Practice★★☆Not started
Graphically represent the solution to the quadratic inequality in two unknowns $y \ge x^2 - 4x + 3$. You can do it on paper and send a photo with your answer.

Graphically represent the solution to the quadratic inequality in two unknowns $y \ge x^2 - 4x + 3$.

You can do it on paper and send a photo with your answer.

Solve

Summary

See all the exercises in this section