### Theory:

Pythagorean Theorem: In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.

In the above right triangle $$ABC$$, the legs are $$AB$$ and $$BC$$, and the hypotenuse is $$AC$$.

So it can be written as, $$AC² = AB² + BC²$$.

Here $$BC = a, AB = b$$ and $$AC = c$$.

Substituting the known values,

$$c² = a² + b²$$.