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Mathematics knowledge point of the second day of junior high school: the area of the circle
The area of a circle is s = π× r× r.

Where π is the peripheral rate, which is equal to 3. 14.

R is the radius of the circle.

The formula for calculating the circumference of a circle is: c = 2π r. C stands for the circumference of a circle and r stands for the radius of a circle. The formula for the area of a circle is: s = π R2 (the square of R). S represents the area of the circle and r is the radius of the circle.

Ellipse circumference calculation formula

Ellipse circumference formula: L=2πb+4(a-b)

Ellipse circumference's Theorem: The circumference of an ellipse is equal to the circumference (2πb) of an ellipse with the radius of the short semi-axis length plus four times the difference between the long semi-axis length (a) and the short semi-axis length (b) of an ellipse.

Elliptic area calculation formula

Elliptic area formula: S=πab

Ellipse area theorem: the area of an ellipse is equal to π times the product of the major semi-axis length (a) and the minor semi-axis length (b) of an ellipse.