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Area of the circle
The area of a circle is p ?r2 or p ?r ?r, where r is the length
of its radius. p is a number that is approximately 3.14159.
Example:
What is the area of a circle having a radius of 4.2 cm, to the
nearest tenth of a square cm? Using an approximation of 3.14159 for
p, and the fact that the area of a circle is p ?r2, the area
of this circle is p ?4.22, that is, 3.14159 ?4.22 =55.41
square cm, which is 55.4 square cm when rounded to the nearest
tenth.
Perimeter of the circle
The perimeter of a circle is called the circumference, and is found
by multiplying the radius of the circle by 2p. p is a special
irrational number that was discovered by the Greeks centuries ago.
It is always involved in finding measurements of circles, cones and
spheres.
Formula: pr2
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