Pythagoras’ Theorem is one of the oldest and most important theory in mathematics.

The first mathematics “textbook” used by teachers, Euclid’s “Elements”, which is the world’s second most published book (after the Bible) contains 13 books, and Pythagoras’ Theorem is the concluding theorem of the first book.

The theorem is stated below. There are hundreds of ways of proving this theorem (in addition to the way that Euclid proves it in his favourite book), which you can find online. It would be good to make a poster to demonstrate and share your favourite proof.

We need to be able to use this theory whenever we see a right-angled triangle to find unknown lengths of sides

**Examples**

**Exercise**

Let’s complete exercise 9I on pages 141 to 142 of the textbook:

The answers are below: