Why does my child think x² + 5x + 6 = (x − 2)(x − 3)?
Your child gets the signs in the brackets the wrong way round when factorising, such as x² + 5x + 6 = (x - 2)(x - 3).
Why children do it
Finding two numbers that multiply to 6 and add to 5 is the right method, and 2 and 3 do. But their signs matter: −2 and −3 also multiply to 6, but add to −5. Multiplying the brackets back out shows whether the signs are right. The answer is (x + 2)(x + 3).
How to help at home
Ask them to multiply their brackets back out: do they give the expression they started with?
The right way
Factorise: x² + 7x + 6
- 1 × 6 = 6Two numbers that multiply to make 6...
- 1 + 6 = 7...and add to make 7.
- (x + 1)(x + 6)Put them in the brackets.
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Start the free checkRelated mistakes
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