https://prepswift.gregmat.com/quizzes/quiz/prepswift-max-area-of-inscribed-polygon (Question 1)Is the answer not 49.999997? which is slightly lesser than 50?
How did you get that?
Most likely they used the GRE calculator. The calculator cannot precisely find the value of \sqrt{2} which means that the result can be very slightly off (as in this case). In other words, they simply didn’t connect the result properly; everything else is fine.