What is the length of the hypotenuse in the triangle below ?

The answer is B. Since you know the lengths of both legs of the triangle, you can use the Pythagorean Theorem to solve. The Pythagorean Theorem says "a squared plus b squared equals c squared. The square root of c is the length of the hypotenuse." Since there is no answer that says 19.799 (This is the approximate answer), then the answer is B.

You have isosceles right triangle or 45-45-90 degree triangle. 

In 45-45-90 triangles hypotenuse = x√2   [x=leg]

If leg = 14cm, then hypotenuse = 14√2 cm.