Answer:
Pythagorean Theorem = a^2 + b^2 = c^2
This is used to solve the hypotenuse of the triangle (the unmarked horizontal side). It takes the sides, which are a and b, and puts them to the power of 2. After that, you take the number, for example lets say 16. You'd find the square root, and that'd be your anwser, (for this example the anwser would be 6).
another example:
side one of triangle (A) (length) = 6
side two of triangle (B) (width) = 8
hypotenuse (C) = ?
(6)^2 + (8)^2 = 36 + 64 = 100. The square root of 100 is 10. C is 10.