Definition: The perimeter or the circumference of the circle is 2pir or 2pi times the radius of the cicrle. It is Pi timies the diameter or pid. Where radius is the constant distance from the centre of the circle to its circumference. Pi is a constant (not rational number) which is like 3.141592654.... For rough calculation, we use it near two .14decimal place value ,3/
Area is pir^2 or pi times the square of the radius. Also in termes of diameter, the area of the cicle is pi(d/2)^2 =pid^2/4.
Therefore, given the the radius or diameter you can find the
area of the cicle.
The semicle : Its perimeter = diameter+(1/2)the circumference =d+(1/2)pid=d(1+pi/2) =2r+pir=r(2+pi).
If a just picture of a cirle is given without giving radius or diameter, and you are required to find its perimeter: Then follow like this:
Draw two non parallel chords AB, CD. A,B,Cand D will be on the circumference of the cicle.
Draw perpendicular bisectors to AB and CD. Let them meet at O. Now O is the centre of the given circle. Then measure OA or OB or OX, where X is any point on the circumference. You will find thar OA=OB=OX = radius. Use the radius in the above given formula to find perimeter or area of circle or semicircle.
No comments:
Post a Comment