Why does my child think the distance from (1, 2) to (4, 6) is 25?
Your child forgets the square root when finding a distance, such as 25 for the distance from (1, 2) to (4, 6).
Why children do it
Pythagoras has three steps: square the changes, add them, then take the square root. 3² + 4² = 25 is where many children stop, but 25 is the distance squared. The distance is √25, which is 5.
How to help at home
Ask them to check against a sketch: is the distance really that long?
The right way
Find the distance between (3, −3) and (19, 9).
- 19 − 3 = 16The change in x.
- 9 − (−3) = 12The change in y.
- √(16² + 12²) = √400Square them, add, and take the square root.
- 20The square root of 400 is 20.
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
- Why does my child divide the wrong way to find a gradient?
- Why does my child get the wrong sign for a gradient?
- Why does my child think the midpoint of (1, 2) and (5, 6) is (6, 8)?
- Why does my child think the midpoint of (1, 2) and (5, 6) is (2, 2)?
- Why does my child think the distance from (1, 2) to (4, 6) is 7?
- Why does my child plot (3, −2) above the x-axis?
- Why does my child write (−4, 3) for the point (3, −4)?