Radius of a circle is half the diameter.
For any given circle draw a straight line from one point on the circulference, through the circle centre, to the opposite point on the circu,afenrece.
Then taking a rule measure the straight line distance. That is the diameter(d)
Half of this distance, that from the circle dentre to the circumference is the radius(r).
r + r = d
or
2r = d
or
r = d/2
From this straight line we can calculate both the area (A)and the circuference(C) by using the following eq'ns/
C = 2pir = pi*d
A = pi *r^(2)
'pi' is a constant for all circles. and the number 3.14 or 3.1416 or 22/7 are used in these APPROXIMATIONS.
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Radius of a circle = diameter/2
We can calculate the area of a circle by using the formula areacircle pi times r2. We know that pi is about 3.14 and r is the radius of the circle. Πr2 Where: Π pi (3.14159265...) r radius of circle
a=3.14xradius squared
The perimeter or circumference of a circle = 2*pi*radius or pi*diameter
The area of a circle is: pi times radius squared