The seventh question! This is the math of the second day of junior high school (the square of mathematics learning method of Hunan Education Edition)
It can be found that the length of ab is a, the length of bd is a square, and bef is an isosceles right triangle. If ef passes through bd and M, bm equals em and mf equals half of ef. Similarly, we can know the relationship in hgd, the half circumference of efgh is equal to the length of bd, and the circumference of efgh is equal to 2 times bd.