Why does my child stop halfway through a box's diagonal?
Your child stops after the first right-angled triangle, such as giving a box's diagonal across its bottom instead of from corner to opposite corner.
Why children do it
Finding the diagonal across the bottom of the box is a whole Pythagoras question on its own, so it feels like the answer. But the rod goes up too: that diagonal and the box's height make a second right-angled triangle, whose hypotenuse is the rod. Sketching each triangle on its own helps.
How to help at home
Ask them to sketch each right-angled triangle on its own: has the one with the answer been used?
The right way
Sam's eyes are 1.5 m above the ground. From 10 m away, the angle of elevation to the top of a tree is 45°. How tall is the tree, to 1 decimal place?
- 11.5Above Sam's eyes, 10 × tan 45° = 10 m. Add the 1.5 m to Sam's eyes: 11.5 m.
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 think sides of 3 and 4 make a hypotenuse of 7?
- Why does my child get a shorter side longer than the hypotenuse?
- Why does my child use the whole base to find an isosceles triangle's height?
- Why does my child mix up the opposite and adjacent sides?
- Why does my child divide when they should multiply in trigonometry?
- Why does my child get sin 30 = −0.988 on the calculator?
- Why does my child get a tiny number when finding an angle?
- Why does my child put the angle of depression in the wrong place?
- Why does my child give 300° for a bearing of 060° the other way?
- Why does my child mix up sin 30° and cos 30°?
- Why does my child think cos 120° = 1/2?
- Why does my child think y = 3 sin x has an amplitude of 6?