Inputs With Signs

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

When the input is negative, put brackets around it. For f(x) = x² - 1, the value at -2 is

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

The whole input replaces x, including its sign. So write -2 in brackets before you square it. The two expressions have different values: (-2)^2 = 4 and -2^2 = -4.

Fractions need the same care. f(1/2) means that the whole fraction 1/2 replaces x in every place where x appears in the rule.

Challenge

Medium

For h(x) = x^2 + 2x, work out h(-4).

Try it yourself

h(-4)

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