The formula of the outer inner circle is: area = (4-π) r * r = (1-π/4) a * a.

The formula of the inner side of the outer circle is: area = (π-2) r * r = (π/2-1) a * a.

The outer circle is the inner side, which is an idiom in China. It refers to the way of dealing with people, which is easy-going on the surface and solemn at heart.

There is a method to find the area of the outer inner circle in the math book taught by the freshmen in the sixth grade of primary school.

The theory of "Fiona Fang" originated from a coin in ancient China, a copper coin inside the outer circle, which was unpretentious, but the ancient sages realized many truths in this small coin.

Extended data

Related formulas of circle and square:

The formula for calculating the circumference of a circle = diameter x3. 14=2x radius x3. 14.

Calculation formula of circular area = radius x radius x3. 14.

1, square c: perimeter s: area a: side length

Perimeter = side length ×4 C=4a

Area = side length × side length S=a×a

2. cube v: volume a: side length

Surface area = side length × side length× ×6 S table =a×a×6 volume = side length× side length× side length v = a× a× a.

Nature of the square:

Special properties: a diagonal of a square divides the square into two isosceles right triangles, and the included angle between the diagonal and the side is 45; The two diagonal lines of a square divide it into four congruent isosceles right-angled triangles.

Other properties 1: Square has all the properties and characteristics of parallelogram, rhombus and rectangle.

Other properties 2: draw the largest circle in a square (inscribed circle of a square), and the area of this circle is about 78.5% of the square area [π]; The area of the smallest circle (circumscribed circle of a square) that completely covers a square is about 157% [π] of the square area.

Other properties 3: A square is a special rectangle and a square is a special diamond.

Baidu Encyclopedia-Foreign Inner Circle

Baidu encyclopedia-outer circle inner side