One Rule, Every Case

A variable lets you write a rule once and reuse it forever. Newton's second law — the relationship we now write as F = ma — applies to every mass and every force, with no need to re-describe each situation in words.

The same abstraction powers computer code. A variable in Python or JavaScript holds a value that can change, while the surrounding logic stays fixed. When a spreadsheet lets you write =A1*B1 instead of retyping numbers, that is algebra at work behind the scenes.