Consider the following statements: Which of the following is correct?

1. In a right-angled triangle, the square on the hypotenuse equals the sum of the squares on the other two sides.
2. If in a triangle $a^2 = b^2 + c^2$, the angle opposite $a$ is a right angle.
3. The theorem of Pythagoras holds only for equilateral triangles.

• ai and ii
• bi and iii
• cii and iii
• di, ii and iii