Add for the hypotenuse, subtract for a shorter side
To find the hypotenuse : . To find a shorter side: — you subtract.
3D Pythagoras = apply it twice
For a space diagonal, find a base diagonal first, then combine it with the height: .
Drawn from real examiner reports.
Adding the squares when you should subtract
When finding a shorter side, students add instead of subtracting, scoring zero for the method.
Rounding a length too early
Rounding an intermediate length (e.g. 6.7 → 7) then using it loses the final accuracy mark.
Identify the hypotenuse first
Mark the right angle; the side opposite it is the hypotenuse. That tells you whether to add or subtract.
In a right-angled triangle with hypotenuse (opposite the right angle):
The single most penalised slip is adding when you should subtract — always identify the hypotenuse (opposite the right angle) first.
How do you find the hypotenuse?
A right-angled triangle has the two shorter sides cm and cm. Find the length of the hypotenuse.
