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Flat and Straight Up

Part of the Graphs & Systems section of Coddy's Algebra journey. Lesson 11 of 61.

Two kinds of line have their own special equations. A horizontal line has rise 0, so its slope is 0. Its equation gives its height: $y = 3$ is the line of all points with y equal to 3. A vertical line has run 0, and you cannot divide by 0, so its slope is undefined. Its equation gives its x value: $x = 2$ is the line of all points with x equal to 2.

$A flat line and a vertical one$

A flat line and a vertical one

Keep the two cases apart. A horizontal line has slope 0, which is a number. A vertical line has no slope at all, because its run is 0 and division by 0 has no value.

Challenge

Easy

Draw the line $x = -3$ .

Try it yourself

x = -3

Draw the line

All lessons in Graphs & Systems

1Points and Rules

Two Numbers, One Point A Rule Makes Points The Points Line Up

4Slope-Intercept Form

y = mx + b The Starting Height Write the Equation Solve for y Draw From Any Form Recap: y = mx + b

7Parallel & Perpendicular

Same Slope, Never Meet The Perpendicular Slope A Right-Angle Line Recap: Two Relations

10Systems by Graphing

Two Lines, One Answer Solve by Drawing Check the Crossing When Lines Never Cross Recap: By Graphing

2The Whole Plane

The Four Quadrants Mirror Points On the Line or Not?Recap: Rule to Line

5Point-Slope Form

A Point and a Slope From Two Points Flat or Vertical Through Draw From a Point Recap: Point-Slope

8Function Notation

The Name of a Rule Inputs With Signs Find the Input The Graph of f Recap: f(x)

11Solving Systems Exactly

Substitution Isolate First Elimination Scale, Then Add Three Unknowns Two Numbers, Two Facts Recap: Two Methods