Math 1 · Unit 2 · Lesson 1
What a Function Is: One In, One Out
A function is a rule where one input gives exactly one output, like a spreadsheet formula. You will learn to read f(x) as f of x, see why y and f(x) are the same thing, and plot points on the coordinate plane by filling in tables and clicking on grids.
The big idea
A function is a promise: one input, one output, every time. A spreadsheet keeps that promise in a cell, and f(x) keeps it on paper. f(x) is read f of x, the formula is what comes after the equals sign, and x is what you feed in. When we graph we usually call the output y instead, but y and f(x) are the same number. Every input and its output make an ordered pair (x, y), and every ordered pair is one dot on the coordinate plane: sideways first, then up or down. Fill a table, plot the rows, and you have graphed the function.
The parts of this lesson
Each part is its own short page. Go in order, or pick the one you need.
Printables
One page with the definition, the spreadsheet picture, f(x) notation with examples, the y and f(x) note, how to plot a point, and a blank grid to fill.