Ok, so the reason we need the Pythagoras theorem is to work out the length of missing side given we know the other 2 sides in a right-angled triangle. (Would go on to draw the triangle with the known sides and unknown side). **The key rule to remember is that 'the hypotenuse squared( c) is equal to the sum of the squares of the other two sides: a**^{2 }**+ b**^{2 }**= c**^{2}. Any questions?Let's proceed to an example. (Would go on to draw an example with numeric values for the sides of the triangle). For instance if shorter sides we 8 and 9. 8^{2}+9^{2}= c^{2} >>>>>>>>>>>>>>>> 145=c^{2}>>>>>>>>>>>>>>>>>145^{1/2}>>>>>>>>>>>>>>>>>>>>>>>>>>>>12.04159458>>>>>>>>>>>>>>>>12.04 (3sf) I will now show an example where the hypotenuse/longest side is known and we want to work out one of the shorter sides.