1) A Pythagorean triples is a set of three integers, a, b, c, that follow the rule a^2 + b^2 = c^2
2) Assumin c is the diagonal of your rectangle and the hypotenuse of the triangles, you are looking this:
13^2 = a^2 + b^2
=> 169 = a^2 + b^2
Two integer numbers that meet that equality are 5 and 12:
5^2 = 25
12^2 = 144
=> 5^2 + 12^2 = 25 + 144 = 169
=> 13^2 = 5^2 + 12^2
Now that you have the three numbers you know the dimensions of the figure and can calculate the area of the shaded part. I cannot do that for you becasue you did not include the figure.
