Go round the calculation

                                                        Go round the calculation

According to the perimeter is equal to solve.

Analysis:

Turn round, hypothesis is the perimeter of party a, then a = 2 PI r, can calculate r.

Then according to the circular area: S = PI r squared, can get the area of a circle.



Extended information:

Circle related formula:

1, round area: S = PI r squared, S = PI (d / 2) squared. The radius for the diameter (d, r).

Semicircle = 2, the area of the semicircle: S (PI r ^ 2) / 2. The radius (r).

3, circle area: S small round circle - S = PI (R ^ 2 - R ^ 2) (for great circle radius R, R) for small circle radius.

4, the perimeter of a circle: C = 2 or PI r C = PI d. The radius for the diameter (d, r).

5, the perimeter of semicircle: d + (d) of PI / 2 or d + PI r. The radius for the diameter (d, r).

6, the fan in the area of a circle divided by n times fan central Angle point of view, 360 are as follows:

S = n / 360 x PI r squared

S = PI r squared x L / 2 PI r = Lr / 2 (L for arc length, radius of r for fan)