Course: Algebra II / Elementary Algebra
Topic: Linear Systems
Subtopic: 3x3 Systems of Equations
Overview
Now that we have the basic process of algebraically solving 2x2 systems down, we are ready to extend our knowledge to include larger linear systems (3x3, 4x4, etc.). Solving a 3x3 system algebraically still uses elimination/substitution methods, but the idea is to eliminate one variable/equation to transform the 3x3 system down to a 2x2 system, solve it, then back substitute to get all there variable answers.
The larger the systems get the more useful using technology to solve them becomes. I strongly recommend that you solve 4x4 and larger systems electronically. Because solving a 3x3 system algebraically is time-consuming, you may want to solve those electronically too (especially on a test), but be sure you know HOW to solve a 3x3 system algebraically.
Solving a linear systems electronically (on a handheld grapher or using a system solver program) requires using a command called RREF. How you do this will depend what technology you have available to you. See the supplemental resources below for suggestions.
Objectives
By the end of this topic you should know and be prepared to be tested on:
- 5.4.1 Solve 3x3 linear systems algebraically (usually by the elimination method, but sometimes the substitution method will work).
- 5.4.2 Solve 4x4 and larger linear systems electronically using a system solver such as RREF.
- 5.4.3 When solving a system electronically using RREF, recognize consistent, inconsistent, and dependent systems.
Terminology
Define: back substitution, matrix, row of a matrix, column of a matrix, size of a matrix (a.k.a. dimension, order), 3x3 system (and 4x4 system, etc.), augmented matrix, row reduced echelon form (RREF)
Text Notes
Text:
Intro & Inter Algebra for CS 3ed by Blitzer, sect. 4.5
- For 3x3 and larger systems, you will only be asked to actually solve those that have a single point answer (the consistent type). For the inconsistent and dependent types, the only thing you need to know is how to recognize them electronically based on the last line of the result from RREF.
- pg 309-310 SKIP the inconsistent and dependent types of systems. It’s neat to look at the geometric aspect of 3x3 systems (i.e. intersecting planes), but if you don’t completely understand them, no problem, it’s covered in later courses.
- pg 310-311 SKIP the modeling applications such as example 4. This includes any problems of the form, "Find the quadratic function y=ax2+bx+c whose graph passes through the given points."
Supplementary Resources
Directions for solving a larger linear system electronically:
- If you have a TI-84/86/89/92 calculator (or other handheld grapher) use the RREF command. See Calculator Guide: Echelon Form.
- If you have a TI-86 calculator, you may use the SIMULT command to solve consistent systems still need the RREF command to identify inconsistent or dependent systems. See Calculator Guide: Linear Systems.
- If you don't have a handheld graphing calculator then use an online row reducer.