Why does my child think x² = 9 only means x = 3?
Your child gives only one solution of a quadratic, which usually has two, such as x² = 9 giving x = 3 but not x = -3.
Why children do it
Most equations children meet have one answer, so they stop at the first. But a negative number squared is positive too, so x = −3 also works: (−3)² = 9. A quadratic usually has two solutions.
How to help at home
Ask: is there another number that works? Try it in the question.
The right way
Solve: (x + 2)(x − 5) = 0
- x + 2 = 0 or x − 5 = 0Either bracket could be the one that's 0.
- x = −2 or x = 5Two solutions: give both.
Find out where your child is
A free maths check, in about 15 minutes, shows what your child knows and the mistakes they make. No sign-up.
Start the free checkRelated mistakes
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