Pythagoras' theorem states that in a right-angled triangle, a squared plus b squared equals c squared, where c is the hypotenuse. To find the hypotenuse, square both shorter sides, add them, then take the square root. For legs of 5cm and 12cm, the hypotenuse is 13cm.
Pythagoras’ theorem connects the three sides of any right-angled triangle: a² + b² = c², where c is the hypotenuse, the side opposite the right angle. It appears on every GCSE paper and underpins trigonometry, so it is worth knowing cold.
Adding when you should subtract. If the hypotenuse is already known, you subtract to find the missing shorter side.
Stopping at the squared value. The answer 169 is c², not c. Always take the square root.
Assuming the hypotenuse is the side drawn longest on the page. Diagrams are rarely to scale, so find the right angle instead.
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