圆公式的面积
圆是距特定点固定距离的点的集合。穿过圆的每条线形成反射对称线。除此之外，它在每个角度都围绕中心旋转对称。圆的一些例子是轮子、比萨饼、圆形地面等。从圆心到圆的距离称为半径。
圆的面积定义为圆在二维平面中所占据的区域。我们可以通过三种方式计算圆的面积。
使用半径的圆面积
Area = πr2
where,
r is the radius and π is the constant value
示例 1：如果圆的半径长度为 3 个单位。计算它的面积。
解决方案：
We know that radius r = 3 units
So by using the above formulae:
Substitute r = 3.
As we know that π value = 3.14
3.14 × 3 × 3 = 28.26
Therefore, The area of the circle is 28.26 squared units.
示例 2：一根大绳子呈圆形。它的半径是 5 个单位。面积是多少？
解决方案：
A large rope is in circular shape means it is similar to circle, so we can use circle formulae to calculate the area of the large rope.
We know that radius r = 5 units
So by using the above formulae:
substitute r = 5.
As we know that π value = 3.14
3.14 × 3 × 3 = 28.26
Therefore, The area of the circle is 78.50 squared units.
使用直径的圆面积
圆的直径是圆半径的两倍，即2r
Area = (π/4) × d2
where,
d is the diameter of the circle.
例1：如果一个圆的直径长度是8个单位。计算它的面积。
解决方案：
We know that diameter = 8 units
so by using the above formulae:
substitute d = 8.
As we know that π value = 3.14
(3.14 /4) × 8 × 8 = 28.26
Therefore, The area of the circle is 50.24 squared units.
例 2：如果绳子的长度为 4 个单位。计算它的面积。
解决方案：
We know that length of rope is in circle. so its diameter= 4 units (given)
so by using the above formulae:
substitute d = 4.
As we know that π value = 3.14
(3.14 /4) × 4 × 4 = 28.26
Therefore, the area of the rope is 12.56 squared units.
使用圆周的圆的面积
周长定义为圆的完整弧的长度。
Area = C2/4π
where,
C is the circumference
示例 1：如果圆的周长是 4 个单位。计算它的面积。
解决方案：
We know that circumference of the circle = 4 units (given)
so by using the above formulae:
substitute C = 4.
As we know that π value = 3.14
4 × 4/(4 × 3.14) = 28.26
Therefore, The area of the circle is 1.273 squared units.
例 2：如果圆的周长是 8 个单位。计算它的面积。
解决方案：
We know that circumference of the circle = 8 units (given)
so by using the above formulae:
substitute C = 8.
As we know that π value = 3.14
8 × 8/(4 × 3.14) = 28.26
Therefore, the area of the circle is 5.09 squared units.