Adventures with Brahmagupta and his Algebraic Proof

Question: Prove Brahmagupta's Formula i.e. that if a cyclic quadrilateral has sides a, b, c, d, and semi-perimeter s, then its area K is given by (...).

Answer:

Professor's commentary: Everything is correct here. However, the proof is not very interesting as you have opted to prove it algebraically rather than with graphical explanation. In fact, it is really boring. In fact, my cat has just thrown up on my trousers and then died out of boredom after having read your proof. I am enraged! Zilch marks for this assignment.