Question

Area of circle?

Answer 1

`A = pir^2 or pi(d/2)^2`

Explanation:

`"Area of a circle" = pir^2`

or

`"Area of a circle" = pi(d/2)^2`

Where;

`A = "Area of a circle"`

`pi = 22/7 or 3.142`

`r = "radius of a circle"`

`d = "diameter of a circle"`

Recall;

`"Diameter of a circle" = "Two radius of a circle"`

`d = 2r`

Hence; `r = d/2`

That's why the Area of a circle is also; `A = pi(d/2)^2`

Answer 2

`Area_circ=pir^2`, where `r` is the radius of the circle;
or
`Area_circ =pi(d/2)^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 `22/7` may be used).