Working Lab
Solve it your way. Every line is checked against the line above it, not against a model answer — so any route that keeps the solutions is correct, including one nobody expected.
Problem
Mode
Each line is checked as you enter it, so a wrong step cannot be built on.
Start
Rule (optional)
Stuck? The ladder never skips to the answer.
What is checking this
A line is valid when it has the same solutions as the line above it. That is the whole test, and it is why the lab has no opinion about which method you use. Where a line is rejected, the engine says which of eleven error classes it matched — and where the evidence fits none of them, it says that instead of guessing.
Current line: 2(x + 3) = 4x − 2