Why does my child think (2x − 3)(x + 4) = 0 gives x = 3?
Your child forgets to divide by the number in front of x, such as 2x − 3 = 0 giving x = 3 instead of x = 3/2.
Why children do it
In the brackets met before, like (x − 3), the number is the answer, so it's natural to read it off. With 2x in the bracket there's one more step: 2x − 3 = 0 gives 2x = 3, so x = 3/2. Putting the answer back in the bracket shows it: 2 × 3 − 3 is 3, not 0.
How to help at home
Ask them to put their answer back into the bracket: does 2 × 3 − 3 come to 0?
The right way
Solve: (2x − 3)(x − 4) = 0
- 2x − 3 = 0 or x − 4 = 0One of the brackets must be 0.
- 2x = 3 or x = 4Solve each one: add 3, or add 4.
- x = 3/2 or x = 4Divide by 2 to finish the first.
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