A circle, Fig. 33, is a plane figure bounded by one uniformly curved line called the circumference. The diameter of a circle is a straight line drawn through the center and terminating at the circumference. The radius is a straight line drawn from the center to the circumference, and is therefore half the diameter.
To find the circumference of a circle from its diameter, multiply the diameter by 3.14159. To find the diameter of a circle from its circumfer-ence, divide the circumference by 3.14159.
Fig. 33 - A Circle.
To find the area of a circle multiply half the circumference by half the diameter, or multiply the square of the diameter by the decimal .7854.
To find the side of the greatest square that can be inscribed in a circle of a given diameter, divide the square of the given diameter by 2 and extract the square root of the quotient.