A classmate solved an equation and is about to write it on the board. Use a quick substitution check to decide: do you trust it, or do you stop them?
4x + 5 = 29
Their answer: x = 6
?Hit “check by substituting” to test their answer.
In the real world nobody hands you the answer key. Verifying is the answer key you carry yourself.
Working backwards: here's an equation with a verified, correct solution. Reconstruct the substitution step that proves it.
3x − 2 = 16
Verified solution: x = 6
To verify, you substitute x = 6 into the left side 3x − 2. What number should the left side come out to?
If your number equals the right-hand side, the solution is verified. That’s the whole point: both sides land on the same number.