What is the hypotenuse?
It is the side of a right angled triangle that is opposite the right angle.
What is Pythagoras’ Theorem?
That a^2 + b^2 = c^ or in other words that the square of the hypotenuse is equal to the sum of the squares of the other two sides.
How can you identify a right angled triangle?
If the triangle follows Pythagoras’ theorem then it is a right angled triangle.