Why does my child think 6x + 9 = 3(2x + 9)?
Your child divides only one term when factorising, such as 6x + 9 = 3(2x + 9).
Why children do it
Factorising takes a common factor out of every term. Children who divide the first term and copy the rest leave the 9 as it was. Expanding the answer checks it: 3(2x + 9) is 6x + 27, not 6x + 9. The right answer is 3(2x + 3).
How to help at home
Ask them to multiply the bracket back out: it should give the expression they started with.
The right way
Factorise: 5x + 45
- 45 = 5 × 95 goes into both 5x and 45.
- 5x + 45 = 5 × x + 5 × 9Write each term as 5 times something.
- 5(x + 9)Take out the 5.
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