Graph Linear Equations
Learning Outcomes
- Create a table of ordered pairs from a two-variable linear equation
- Graph a two-variable linear equation using a table of ordered pairs
- Determine whether an ordered pair is a solution of an equation
Example
Describe the point shown as an ordered pair.Answer: Begin at the origin and move along the x-axis. This is the x-coordinate and is written first in the ordered pair.
([latex]5, y[/latex])
Move from [latex]5[/latex] up to the ordered pair and read the number on the y-axis. This is the y-coordinate and is written second in the ordered pair.([latex]5, 2[/latex])
The ordered pair of the point is ([latex]5, 2[/latex]).Example
Plot the point [latex](−4,−2)[/latex].Answer: The x-coordinate is [latex]−4[/latex] because it comes first in the ordered pair. Start at the origin and move [latex]4[/latex] units in a negative direction (left) along the x-axis. The y-coordinate is [latex]−2[/latex] because it comes second in the ordered pair. Now move [latex]2[/latex] units in a negative direction (down). If you look over to the y-axis, you should be lined up with [latex]−2[/latex] on the axis. Draw a point at this location and label the point [latex](−4,−2)[/latex].
Plotting Points to Graph Linear Relationships
x-coordinate | y-coordinate |
[latex]0[/latex] | [latex]0[/latex] |
[latex]1[/latex] | [latex]2[/latex] |
[latex]2[/latex] | [latex]4[/latex] |
[latex]3[/latex] | [latex]6[/latex] |
[latex]4[/latex] | [latex]8[/latex] |
Example
Graph the linear equation [latex]y=2x+3[/latex].Answer: Evaluate [latex]y=2x+3[/latex] for different values of x, and create a table of corresponding x and y values.
x values | [latex]2x+3[/latex] | y values | Ordered Pairs |
[latex]0[/latex] | [latex]2(0) + 3[/latex] | [latex]3[/latex] | ([latex]0, 3[/latex]) |
[latex]1[/latex] | [latex]2(1) + 3[/latex] | [latex]5[/latex] | ([latex]1, 5[/latex]) |
[latex]2[/latex] | [latex]2(2) + 3[/latex] | [latex]7[/latex] | ([latex]2, 7[/latex]) |
[latex]3[/latex] | [latex]2(3) + 3[/latex] | [latex]9[/latex] | ([latex]3, 9[/latex]) |
Ordered Pairs as Solutions
So far, you have considered the following ideas about lines: a line is a visual representation of a linear equation, and the line itself is made up of an infinite number of points (or ordered pairs). The picture below shows the line of the linear equation [latex]y=2x–5[/latex] with some of the specific points on the line. Every point on the line is a solution to the equation [latex]y=2x–5[/latex]. You can plug the ordered pair [latex](1,−3)[/latex] into the equation and the equation will be satisfied.[latex]\begin{array}{l}\,\,\,\,y=2x-5\\-3=2\left(1\right)-5\\-3=2-5\\-3=-3\\\text{This is true.}\end{array}[/latex]
You can also plug ANY of the other points on the line into the equation. Every point on the line is a solution to the equation [latex]y=2x–5[/latex]. All this means is that determining whether an ordered pair is a solution of an equation is pretty straightforward. If the ordered pair is on the line created by the linear equation, then it is a solution to the equation. But if the ordered pair is not on the line—no matter how close it may look—then it is not a solution to the equation. To find out whether an ordered pair is a solution of a linear equation, you can do the following:- Graph the linear equation and graph the ordered pair. If the ordered pair appears to be on the graph of a line, then it is a possible solution of the linear equation. If the ordered pair does not lie on the graph of a line, then it is not a solution.
- Substitute the (x, y) values into the equation. If the equation yields a true statement, then the ordered pair is a solution of the linear equation. If the ordered pair does not yield a true statement then it is not a solution.
Example
Determine whether [latex](−2,4)[/latex] is a solution to the equation [latex]4y+5x=3[/latex].Answer: For this problem, you will use the substitution method. Substitute [latex]x=−2[/latex] and [latex]y=4[/latex] into the equation.
[latex]\begin{array}{r}4y+5x=3\\4\left(4\right)+5\left(−2\right)=3\end{array}[/latex]
Evaluate.[latex]\begin{array}{r}16+\left(−10\right)=3\\6=3\end{array}[/latex]
The statement is not true, so [latex](−2,4)[/latex] is not a solution to the equation [latex]4y+5x=3[/latex].Licenses & Attributions
CC licensed content, Shared previously
- Graph Basic Linear Equations by Completing a Table of Values. Authored by: mathispower4u. License: All Rights Reserved. License terms: Standard YouTube License.
- Determine If an Ordered Pair is a Solution to a Linear Equation. Authored by: mathispower4u. License: All Rights Reserved. License terms: Standard YouTube License.
- Plot Points Given as Ordered Pairs on the Coordinate Plane. Authored by: James Sousa (Mathispower4u.com) for Lumen Learning. License: CC BY: Attribution.