Solution: Because the included angle between two diagonal lines of a rectangle is 60 degrees,

So the four included angles of an equilateral angle are all 60 degrees,

Because this quadrilateral is rectangular,

So half of the two diagonals are equal, and all four triangles in the rectangle are isosceles triangles.

Because two triangles in the rectangle are isosceles triangles, one angle is equal to 60.

So two triangles in a rectangle are equilateral triangles,

The side length of a rectangle is equal to 2× 1/2 = 1,

According to Pythagorean theorem, the square of the other side of the rectangle with the length of root number 2 minus the square of 1 is equal to root number 3.

The circumference of a rectangle is equal to 2× 1 plus 2× root number 3 = 2 root number 3+2.

This is the case when the sides and lengths of the rectangle are different.

When the sides of a rectangle are equal (square), the circumference is four.

This is just my personal opinion, for reference only! It would be better if there were pictures!