A basic theorem for finding the third length of a right angle triangle is the Pythagoras Theorem.
In a right angle triangle, the slant and usually longest side is called the Hypotenuse while the other two sides are Opposite and Adjacent.
The Pythagoras Theorem States:
Step-by-step explanation:
If for example, we are given the other two sides as 3 and 4 respectively,
Using
Hypotenuse = =5
These set of numbers (3,4,5) in this  that satisfies the theorem are called Pythagorean Triples