We are only able to come up with 2 equations using the obvious relationship between semicircle and square. But we have x, y and z variables.
How do we proceed?
Thanks to my girlfriend, who came up with the solution:
The tiny small shaded area can be calculated by substracting the isosceles triangle (等腰三角形) from a 1/12 circle.
And the tiny small shaded area is simply a part of the larger shaded area.
Do you own math.