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Course: Algebra I / Elementary Algebra
Topic: Lines and their Graphs
Subtopic: Equations of Lines II - Point-Slope Formula

Overview

There are two formulas that can be used to find the equation of a line, the slope-intercept formula y=mx+b and the point-slope formula y-y1=m(x-x1). Which you use depends on the information you know about the line. If you know the slope m and the y-intercept value b, plug those into the slope-intercept formula to get the equation of the line. If you know a point on the line (x1,y1) and the slope m of the line, plug them into the point-slope formula, then solve it for y to get the equation of the line.

Objectives

By the end of this topic you should know and be prepared to be tested on:

• 4.4.1 Given the slope and a point on the line (either the y-intercept or one that is not the y-intercept), find its equation
• 4.4.2 Given two points on a line, find its slope then equation
• 4.4.3 Understand applications of the equation of the line

Terminology

Point-Slope Formula for the equation of a line y-y1=m(x-x1) (memorize it!)

Text Notes

This whole "lines" chapter is filled with important formulas, terminology, and processes. Spend significant time learning them well. The next chapter deals with "systems of linear equations" where the graphs will have more than one linear equation and we will be analyzing how they connect including finding intersection points and interpreting this information in terms of fairly advanced applications. I cannot stress enough how important it is to have the processes of "equation -> graph" and "graph -> equation" down well before we start adding the additional lines to form multi-equation multi-variable systems!