Why does my child divide when they should multiply in trigonometry?
Your child divides when the unknown is on top, such as working out x = 12 sin 35° as 12 ÷ sin 35°, or multiplies when it's underneath.
Why children do it
The ratio, sin 35° = x ÷ 12, has a division in it, so dividing feels right. But x is on top, so it's undone by multiplying: x = 12 × sin 35°. When x is underneath, sin 35° = 12 ÷ x, it's the other way: x = 12 ÷ sin 35°. Writing the ratio as a fraction first shows which.
How to help at home
Ask them to write the ratio as a fraction first, x/12 or 12/x, then undo it.
The right way
Find x, to 1 decimal place.
- 6.9Opposite and hypotenuse: x = 12 × sin 35° = 6.88..., which is 6.9.
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