Which special version of the pythagorean theorem can you use to find the length of any square's

The Pythagorean Theorem states that "When a triangle has a right angle of (90°), the square of its hypothenuse is equal to the sum of the squares of the other two sides."

The hypothenuse is the longest side of the triangle.

For example: A triangle has 3 sides. Side A, Side B, and Side C (hypothenuse).

Side A = 3; Side B = 4; Side C = 5; To check if the theorem is true, we must square all sides.

Side A = 3² = 9; Side B = 4² = 16; Side C = 5² = 25

Pythagorean theorem: The square of the hypothenuse is equal to the sum of the squares of two sides.

Side A² + Side B² = Side C²  ==> 9 + 16 = 25 ==> 25 = 25

 

It says in the questions that it is 6.5?