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Flat and Straight Up

Part of the Graphs & Systems section of Coddy's Algebra journey. Lesson 14 of 64.

Two special directions get special equations. A flat line has rise 0, so its slope is 0 and its equation names its height: y = 3 is every point at height 3. A vertical line has run 0, and dividing by 0 is impossible: its slope is undefined, and its equation names its column: x = 2.

$A flat line and a vertical one$

A flat line and a vertical one

The names are worth keeping apart: slope 0 is a perfectly good slope (flat), while a vertical line has no slope at all. One is a number, the other is the absence of one.

Challenge

Draw the line x = -3.

Try it yourself

x = -3

Draw the graph

Test yourself

This lesson includes a short quiz. Start the lesson to answer it and track your progress.

All lessons in Graphs & Systems

1The Coordinate Plane

Two Numbers, One Point The Four Quadrants Points on the Axes Mirror Points Recap: The Plane

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

2From Rule to Line

A Rule Makes Points The Points Line Up On the Line or Not?Between the Dots 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