All the equations we solved so far have been equations with one variable. In almost every case, when we solved the equation we got exactly one solution. The process of solving an equation ended with a statement such as x=4. Then we checked the solution by substituting back into the equation.
Here’s an example of a linear equation in one variable, and its one solution.
Linear Equation
An equation of the form
Ax+By=C, where
AandB are not both zero, is called a linear equation in two variables.
Notice that the word "line" is in linear.
Here is an example of a linear equation in two variables,
Solution to a Linear Equation in Two Variables
An ordered pair
(x,y) is a solution to the linear equation
Ax+By=C, if the equation is a true statement when the
x- and
y-values of the ordered pair are substituted into the equation.
example
Determine which ordered pairs are solutions of the equation
x+4y=8:
1.
(0,2)
2.
(2,−4)
3.
(−4,3)
Solution
Substitute the
x- andy-values from each ordered pair into the equation and determine if the result is a true statement.
1. (0,2) |
2. (2,−4) |
3. (−4,3) |
x=0,y=2
x+4y=8
0+4⋅2=?8
0+8=?8
8=8✓ |
x=2,y=−4
x+4y=8
2+4(−4)=?8
2+(−16)=?8
−14=8 |
x=−4,y=3
x+4y=8
−4+4⋅3=?8
−4+12=?8
8=8✓ |
(0,2) is a solution. |
(2,−4) is not a solution. |
(−4,3) is a solution. |
example
Determine which ordered pairs are solutions of the equation.
y=5x−1:
1.
(0,−1)
2.
(1,4)
3.
(−2,−7)
Answer:
Solution
Substitute the x- and y-values from each ordered pair into the equation and determine if it results in a true statement.
1. (0,−1) |
2. (1,4) |
3. (−2,−7) |
x=0,y=−1
y=5x−1
−1=?5(o)−1
−1=?0−1
−1=−1✓ |
x=1,y=4
y=5x−1
4=?5(1)−1
4=?5−1
4=4✓ |
x=−2,y=−7
y=5x−1
−7=?5(−2)−1
−7=?−10−1
−7=−11 |
(0,−1) is a solution. |
(1,4) is a solution. |
(−2,−7) is not a solution. |