Pythagorean theorem — introduction (Year 7)

First encounter with the Pythagorean theorem in a right triangle: find the hypotenuse, find a missing leg, and apply the theorem in a short word problem about a ladder leaning against a wall. For 1.º ESO (EN gets an introduction article only — the formal Pythagorean theorem unit lives in Year 8/9 in the UK/US curricula).