<p>As for the way I solved it… I assumed the area of a semicircle as pi.d^2/4 so when u add both AC^2 and AB^2 using the Pythagorean theorem you are going to end up with k^2 so you substitute and you’ll get 2pi.k^2/16 which simplifies to the formula pi.k^2/8 and it’s the right answer… @SATQuantum I didn’t really understand how u got the pi.AC^2/8 instantly as I got 4 in the denominator ?? Can u please explain your way to me…</p>