Variables & Expressions
📋 What it is
A variable stands for the input; an expression like 2x + 1 is the rule written in symbols.
🗣️ Coach says
Once you name the input x, the rule becomes an expression: "double it and add one" is 2x + 1. Writing the rule in symbols lets you compute any output instantly, without a table.
🧠 Memory hook
The rule in words → the rule in symbols. "double and add 1" = 2x + 1.
😂 Giggle
Why did the number go through the function machine?
To get transformed!
😲 Whoa!
The letter x for "unknown" was popularised by Descartes in the 1630s and stuck for nearly 400 years.
✅ Quick check: Write "triple the input, then subtract 2" as an expression using x.
Say your answer out loud first — then reveal.
3x − 2.
"Triple" means ×3 and "subtract 2" means −2, applied to the input x.
🧪 Try it! (2 minutes)
Turn "add 4 then halve it" into an expression, then test it with x = 6.