Lesson 5 of 48
Balancing equations
The equals sign is a constraint, not an instruction to compute.
In code `x = x + 1` is an order. In mathematics `x = x + 1` is a claim, and a false one. Reading `=` as “these two things are the same” is what makes algebra manipulable rather than memorised.
Do this
Solve a multi-step linear equation and justify every line by naming the operation you applied to both sides. Then take a wrong worked solution and find the exact line where it broke.
The question that unlocks the next lesson
Why can you subtract 3 from both sides of an equation?
- ABecause subtraction undoes addition
- BBecause doing the same thing to two equal things leaves them equal
- CBecause the 3 was on the wrong side
- DBecause you may only move constants, never variables