# Write a linear inequality for the graph

Systems of Equations and Inequalities In previous chapters we solved equations with one unknown or variable. We will now study methods of solving systems of equations consisting of two equations and two variables. Represent the Cartesian coordinate system and identify the origin and axes. Systems of Equations and Inequalities In previous chapters we solved equations with one unknown or variable. We will now study methods of solving systems of equations consisting of two equations and two variables.

Represent the Cartesian coordinate system and identify the origin and axes. Given an ordered pair, locate that point on the Cartesian coordinate system. Given a point on the Cartesian coordinate system, state the ordered pair associated with it.

We have already used the number line on which we have represented numbers as points on a line. Note that this concept contains elements from two fields of mathematics, the line from geometry and the numbers from algebra. Rene Descartes devised a method of relating points on a plane to algebraic numbers. This scheme is called the Cartesian coordinate system for Descartes and is sometimes referred to as the rectangular coordinate system. This system is composed of two number lines that are perpendicular at their zero points.

Perpendicular means that two lines are at right angles to each other. Study the diagram carefully as you note each of the following facts. The number lines are called axes. The horizontal line is the x-axis and the vertical is the y-axis. The zero point at which they are perpendicular is called the origin.

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Positive is to the right and up; negative is to the left and down. The arrows indicate the number lines extend indefinitely. Thus the plane extends indefinitely in all directions. The plane is divided into four parts called quadrants. These are numbered in a counterclockwise direction starting at the upper right.

Points on the plane are designated by ordered pairs of numbers written in parentheses with a comma between them, such as 5,7.

This is called an ordered pair because the order in which the numbers are written is important. The ordered pair 5,7 is not the same as the ordered pair 7,5. Points are located on the plane in the following manner.

First, start at the origin and count left or right the number of spaces designated by the first number of the ordered pair.

## Graphing Linear Inequalities

Second, from the point on the x-axis given by the first number count up or down the number of spaces designated by the second number of the ordered pair. Ordered pairs are always written with x first and then y, x,y.

The numbers represented by x and y are called the coordinates of the point x,y. The first number of the ordered pair always refers to the horizontal direction and the second number always refers to the vertical direction.

Check each one to determine how they are located. What are the coordinates of the origin? Find several ordered pairs that make a given linear equation true. Locate these points on the Cartesian coordinate system.Fit an algebraic two-variable inequality to its appropriate graph.

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If one point of a half-plane is in the solution set of a linear inequality, then all points in that half-plane are in the solution set. This gives us a convenient method for graphing linear inequalities.

To graph a linear inequality 1. Replace the inequality symbol with an equal sign and graph the resulting line.

2. Fit an algebraic two-variable inequality to its appropriate graph. Modeling with linear inequalities. Practice: Two-variable inequalities from their graphs. This is the currently selected item.

## Related Content

Intro to graphing systems of inequalities. Graphing systems of inequalities. To graph the solution to this system we graph each linear inequality on the same set of coordinate axes and indicate the intersection of the two solution sets.

Note that the solution to a system of linear inequalities will be a collection of points. We explain Writing a Linear Inequality from a Graph with video tutorials and quizzes, using our Many Ways(TM) approach from multiple teachers.

## Graphing Linear Inequalities

This lesson will demonstrate how to write a linear inequality from a graph. For each country, write a linear inequality and graph it using initiativeblog.com Use the graph to decide on the number of food packages and medicine packages that each country should give.

(all countries should give the same amount each).

Two-variable inequalities from their graphs (practice) | Khan Academy