Geometry · JSS 3
Pythagoras' theorem
Find a missing side of a right-angled triangle.
- c2 = a2 + b2
What the letters mean
- c
- the hypotenuse (longest side, opposite the right angle)
- a, b
- the two shorter sides
Worked example
The two shorter sides of a right-angled triangle are 6 cm and 8 cm. Find the hypotenuse.
Step 1: Square and add
c2 = 62 + 82 = 36 + 64 = 100
Step 2: Square root
c = √100 = 10 cm
Final answer: 10 cm
To find a shorter side, subtract: a2 = c2 − b2.
See it
Play with this picture from the Pythagoras' Theorem lesson.
60° + 48° + 72° = 180°
This is an acute-angled, scalene triangle. Drag any corner!
Put the three angles together and they make a straight line: 180°.
Your task: make a right-angled triangle
Drag a corner until one angle shows 90°. Tip: line two sides up with the grid lines.