Using inverse operations
Recognise inverse relationships between operations and use them to check answers and simplify calculations.
What a learner can do afterwards
- Use addition and subtraction as inverse operations to check and solve problems
- Use multiplication and division as inverse operations to check and solve problems
- Recognise that squaring and square-rooting are inverse operations
1 · Read
An inverse operation undoes another operation. Subtraction undoes addition, division undoes multiplication, and square-rooting undoes squaring. If you know one fact, the inverse gives you another fact.
Zara works out 90 ÷ 9 = 10. She checks with the inverse, 10 × 9, which gives 90 and confirms her answer.
The same trick works with addition and subtraction. If 156 + 27 = 183, you can check it with the inverse: 183 - 27. That should bring you straight back to 156.
Squaring and square-rooting are inverses too: 8² = 64, and √64 = 8. After a calculation, ask which inverse operation can check it. This is often faster than doing the whole calculation again.
Every operation has an inverse that undoes it, so use the inverse to check your answer instead of starting over.
ExtraItems and media are imported from the hoofer-content corpus; per-item provenance is in the file. The rewritten readings were written for this dataset. Enrichment flashcards are derived from facts-collection candidates and are not individually provenance-tracked. Corpus CC0 labels are not publisher proof.
2 · Watch
Take it off screen
Where it sits
17 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.