This question tests rearranging Pythagoras' Theorem to find a shorter side of a right-angled triangle.
Subtract the square of the known side from the hypotenuse squared, then take the square root.
When one side and the hypotenuse are known in a right-angled triangle, the missing side can be found by rearranging Pythagoras' Theorem: b^2 = c^2 - a^2, then b = √(c^2 - a^2). This skill is essential for problem-solving in GCSE geometry, ensuring accurate calculations and logical reasoning when determining distances or sides. Practising this rearrangement develops algebraic manipulation skills and confidence in applying the theorem.