By doing the Pythagorean theory, A^2 + B^2= C^2, you are proving that the triangle is a right triangle with the right angle across from the longest side, so
24^2 + 10^2 = 26^2
576 + 100 = 676, which is true, that means angle B is a right angle. Tangents touch the side of the circle at a right angle, so BC is perpidicular to AB.
A is true