是算出来的。没有看出直观图形
假设大阴影x 小阴影y, 小圆a, 右边空b。左上c
a = π
b+y=8,
c+y=大方型-大圆/4 = 16 - 4π
b-c = 8-(16 -4π)= 4π - 8
a+c+x = b+y
x-y = b-c -a = 4π - 8 - π = 3π - 8