Balance · 12 of 13

A letter is a closed box

x is a name for an amount you haven’t pinned down.

Why this exists

Sometimes you know a relationship before you know a number. Three jars hold the same number of coins, and together they hold 12. You can talk about a jar before you open it.

A letter is the label on the jar. It is not a different species of mathematics, and it is not a code you’re failing to crack.