# System of Equations

Pronunciation: /ˈsɪs.təm ʌv ɪˈkweɪ.ʒənz/ Explain
 y = x2 - 3 y = 2x + 1 Figure 1: A system of equations

A system of equations is a set of equations that are taken to be simultaneously true. A system of equations is also called simultaneous equations. If a system of equations contains only linear equations is a linear system.

A system of equations may have no solution. This means that there are no values for which all the equations are true at once. A system of equations may have one or more solutions. The solution(s) of the system of equations are any values for which all the equations are simultaneously true.

### Visualizing a System of Equations

 Click the line and parabola and drag them to change the figure. Move the line and parabola so that there are no soultions, one solution and two solutions. With a line and parabola, can there be more than two solutions? Why? Manipulative 1 - Simultaneous Equations Created with GeoGebra.

A system of equations can be visualized by graphing the equations. The solution(s) of the system are the points of intersections of the curves. If the graphs of the equations do not intersect, the system has no solutions.

The figure in manipulative 1 shows two simultaneous equations. The parabola is green and the line is blue. The red points are the points of intersection. The values of the red points are the solutions to the system. Click on the line and the parabola and drag them to change the figure.

#### Discovery

What is the greatest number of solutions that can be found for a system consisting of a line and a parabola?

### How to Solve a System of Equations Using Substitution

A system of equations can often be solved by substitution. One variable is replaced by an expression equal to that variable. Take the system of equations StepEquationsDescription
1 These are the simultaneous equations to solve.
2 Use the substitution property of equality to substitute x + 1 in for y.
3 Since the resulting equation in step 2 is a quadratic, we will be using the quadratic formula to solve it. The quadratic formula requires a zero be on one side of the equation. Use the additive property of equality to add -x - 1 to both sides. Use the associative property of addition to get like terms next to each other. Combine like terms. Use the additive property of zero to simplify the left side of the equation.
4 Apply the quadratic formula with a = 1, b = -1 and c = -2. Use the definition of negation to simplify the double negative. Simplify the exponent. Simplify multiplication and division. Simplify addition and subtraction. Simplify the square root. Split the plus or minus into two equations. Split addition and subtraction. Simplify the fractions. These are the possible values of x.
5 Use the substitution property of equality to substitute 2 in for x. Perform the substitution. Simplify the addition. One solution of the system is the ordered pair (2, 3).
6 Use the substitution property of equality to substitute -1 in for x. Perform the substitution. Simplify the addition. One solution of the system is the ordered pair (-1 ,0).
Table 1: Solving simultaneous equations

1. McAdams, David E.. All Math Words Dictionary, system of equations. 2nd Classroom edition 20150108-4799968. pg 174. Life is a Story Problem LLC. January 8, 2015. Buy the book

• McAdams, David E.. Linear System. allmathwords.org. All Math Words Encyclopedia. Life is a Story Problem LLC. 3/12/2009. http://www.allmathwords.org/en/l/linearsystem.html.

McAdams, David E. System of Equations. 5/7/2019. All Math Words Encyclopedia. Life is a Story Problem LLC. http://www.allmathwords.org/en/s/systemofequations.html.

### Revision History

5/7/2019: Changed equations and expressions to new format. (McAdams, David E.)
12/21/2018: Reviewed and corrected IPA pronunication. (McAdams, David E.)