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Area of circle?

Mar 8, 2018

$A = \pi {r}^{2} \mathmr{and} \pi {\left(\frac{d}{2}\right)}^{2}$

Explanation:

$\text{Area of a circle} = \pi {r}^{2}$

or

$\text{Area of a circle} = \pi {\left(\frac{d}{2}\right)}^{2}$

Where;

$A = \text{Area of a circle}$

$\pi = \frac{22}{7} \mathmr{and} 3.142$

$r = \text{radius of a circle}$

$d = \text{diameter of a circle}$

Recall;

$\text{Diameter of a circle" = "Two radius of a circle}$

$d = 2 r$

Hence; $r = \frac{d}{2}$

That's why the Area of a circle is also; $A = \pi {\left(\frac{d}{2}\right)}^{2}$

Mar 8, 2018

$A r e {a}_{\circ} = \pi {r}^{2}$, where $r$ is the radius of the circle;
or
$A r e {a}_{\circ} = \pi {\left(\frac{d}{2}\right)}^{2}$, where $d$ is the diameter of the circle.

Explanation:

Other formulae are possible depending upon what information you have been given about the circle (for example, you might be given 3 points on the circumference of the circle).

However, these are the most common forms.

Note that $\pi$ is an irrational value, approximately equal to $3.14159$ (sometimes for non-critical approximations the ratio $\frac{22}{7}$ may be used).