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ESO Y4B · Mathematics
Equations and systems · Equations, inequalities and systems

Non-linear systems of equations

The perimeter of a rectangle is $28$ cm and its area is $48$ cm². Once again we have two unknowns and two equations, but now one of them contains a product of unknowns instead of a sum. It is no longer linear: it is a non-linear system, and it needs a slightly different strategy.

Before you start, make sure you know: Quadratic equations (3rd ESO)
Before you start, make sure you know: Systems of equations (3rd ESO)

What a non-linear system is

System bracket showing a linear equation that is easy to rearrange and a non-linear quadratic equation. x − y = 2(linear, easy to rearrange) x² + y² = 34(non-linear)
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Solve the system formed by a linear equation and a quadratic equation: $x - y = 2$ $x^2 + y^2 = 34$

Solve the system formed by a linear equation and a quadratic equation:

$x - y = 2$

$x^2 + y^2 = 34$

Solve
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Solve the following system: $x^2 - y^2 = 16$ $x + y = 8$

Solve the following system:

$x^2 - y^2 = 16$

$x + y = 8$

Solve

Line and curve: how many points of intersection

A linear equation is a line; an equation with $x^2$ (and no $y^2$) is a parabola. A line–parabola system can have two, one or no real solutions, depending on the discriminant of the quadratic equation that results from substituting.

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Solve the following system of non-linear equations: $y = x^2 - 4x$ $y = x - 6$

Solve the following system of non-linear equations:

$y = x^2 - 4x$

$y = x - 6$

Solve
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Solve the following system containing a radical equation: $x + y = 10$ $\sqrt{x} - y = -4$

Solve the following system containing a radical equation:

$x + y = 10$

$\sqrt{x} - y = -4$

Solve

Symmetric systems: sum and product, sum of squares

Symmetric system formed by the equations x + y = 15 (sum) and x · y = 56 (product). x + y = 15 & x · y = 56
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Find the solution to the system: $x + y = 7$ $x \cdot y = 12$

Find the solution to the system:

$x + y = 7$

$x \cdot y = 12$

Solve
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The sum of the squares of two numbers is $25$, and one of them is $1$ unit less than the other. Set up a system of equations and find the numbers.

The sum of the squares of two numbers is $25$, and one of them is $1$ unit less than the other. Set up a system of equations and find the numbers.

Solve
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Solve the following symmetric system of equations: $x^2 + y^2 = 25$ $x \cdot y = 12$

Solve the following symmetric system of equations:

$x^2 + y^2 = 25$

$x \cdot y = 12$

Solve

Geometry problems: perimeter and area

In rectangles, rhombuses and other shapes, the perimeter usually gives a linear equation, and the area (or the diagonal, using Pythagoras) gives a non-linear equation.

Rectangle with sides x and y and the algebraic expressions for its area and perimeter. x y A = x · y = 48 P = 2x + 2y = 28
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The product of two positive integers is $156$ and one is consecutive to the other. Set up a system of equations and find these numbers.

The product of two positive integers is $156$ and one is consecutive to the other. Set up a system of equations and find these numbers.

Solve
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The area of a rectangular rug is $6 \text{ m}^2$ and its perimeter measures $10 \text{ m}$. Set up a system of non-linear equations and calculate the dimensions of the…

The area of a rectangular rug is $6 \text{ m}^2$ and its perimeter measures $10 \text{ m}$. Set up a system of non-linear equations and calculate the dimensions of the rug.

Solve
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The hypotenuse of a right-angled triangle measures $13 \text{ cm}$. It is known that one leg is $7 \text{ cm}$ longer than the other. Set up a system of non-linear…

The hypotenuse of a right-angled triangle measures $13 \text{ cm}$. It is known that one leg is $7 \text{ cm}$ longer than the other. Set up a system of non-linear equations to calculate the length of the two legs.

x y 13
Solve

Checking the solutions in their context

A non-linear system can have several mathematical solutions, but not all of them make sense in a real-life problem.

Flowchart illustrating the discarding of mathematical solutions that do not fit the real-life context. mathematical solutions: x = 6 or x = −4 x = length → discard x = −4
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A group of students buys a present for a classmate for $120$ euros, sharing the cost equally. At the last minute, $2$ more students join, which means each of the…

A group of students buys a present for a classmate for $120$ euros, sharing the cost equally. At the last minute, $2$ more students join, which means each of the original students pays $3$ euros less. How many students were there at the beginning and how much did each pay?

Solve
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A piece of wire $40 \text{ cm}$ long is cut into two pieces. One of the pieces is used to form a square and the other to form a rectangle whose base is twice its height.…

A piece of wire $40 \text{ cm}$ long is cut into two pieces. One of the pieces is used to form a square and the other to form a rectangle whose base is twice its height. If the sum of the areas of both shapes is $48 \text{ cm}^2$, how long is each piece of wire?

Solve
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In a park, a rectangular play area will be built surrounded by an artificial grass path of width $1 \text{ m}$ along its entire perimeter. The area of the play area must…

In a park, a rectangular play area will be built surrounded by an artificial grass path of width $1 \text{ m}$ along its entire perimeter. The area of the play area must be $48 \text{ m}^2$ and the total area (play area plus path) must be $96 \text{ m}^2$. Set up a system of equations to find the dimensions of the play area.

Area = 48 m2 Total area = 96 m2 1 m 1 m x y
Solve

Summary

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