# Always check Solving is only half. **Checking** proves it. Solved `2x − 3 = 7` and got `x = 5`? Left side: `2(5) − 3 = 10 − 3 = 7` Right side: `7` Equal → solution is correct. If they disagree, you made a slip. Do not erase the whole page — find the line where both sides stopped matching. > Exam habit: write “Check:” and one line. Examiners love it. You will love it when it saves marks. ## Checking is the second half of solving A finished bookwork should look like: ``` 2x − 3 = 7 2x = 10 x = 5 Check: 2(5) − 3 = 7 ✓ ``` Without the last line you have a guess with extra writing. ### When the check fails 1. Recompute the check — maybe the check had the slip 2. If the check is right and still fails, walk up your steps 3. The first line where left ≠ right (after a legal move) is the bug ### Exam habit Even if you are sure, write Check. It is the cheapest mark-saver in algebra.