Inputs With Signs

Part of the Graphs & Systems section of Coddy's Algebra journey. Lesson 38 of 64.

Substituting a negative input deserves brackets. For f(x) = x² - 1 the value at -2 is

f(-2) = (-2)^2 - 1 = 3

because the whole input, sign included, goes where the x was. Dropping the brackets invites -2² = -4, the classic wrong turn from the Fundamentals section.

The same care applies to fractions: f(1/2) means the entire 1/2 replaces x everywhere it appears, however many appearances there are.

Challenge

The rule is h(x) = x² + 2x. Work out h(-3).

Try it yourself

h(-3)

Simplify the expression

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 RuleInputs With SignsFind 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