area of a circle..

knightdrak01 · 2009-12-03 22:48:13

plz i really need help and the question is:

A circle has a perimeter of p cm. Its area, in square centemetres is :
(a) p squared/ 4 times pi
(b) p squared / 4
(c) pi times p squared
(d) 2 times pi times p
(e) 2 times pi / p

p.s sori for the writting but i need help on it....

Last edited by knightdrak01 (2009-12-03 22:49:01)

mathsyperson · 2009-12-03 22:53:44

If the radius of the circle is r, then:
- Its perimeter is 2πr
- Its area is πr²

You're told the perimeter, so you need to first get the radius in terms of that, then use that answer to find the area.

rohit · 2009-12-03 23:41:01

hi
answer is (b)

because p=2(pi)r
=>r=p/2(pi)
so area=(pi)*r2
=p^2/4(pi)

knightdrak01 · 2009-12-04 20:19:49

how did u work out the radius? huh?!

mathsyperson · 2009-12-04 21:57:41

p = 2πr

So rearranging, that becomes r = p/(2π).

knightdrak01 · 2009-12-05 22:24:37

but p is NOT the diameter!!! it is the CIRCUMFERENCE!!

Devantè · 2009-12-05 22:31:31

Yes, and what is the formula for the circumference of a circle?

Last edited by Devantè (2009-12-05 22:31:49)

knightdrak01 · 2009-12-12 17:36:11

2 pi radius

knightdrak01 · 2009-12-12 17:37:12

guys its asking for the area in square centimeters

Math Is Fun Forum

#1 2009-12-03 22:48:13

area of a circle..

#2 2009-12-03 22:53:44

Re: area of a circle..

#3 2009-12-03 23:41:01

Re: area of a circle..

#4 2009-12-04 20:19:49

Re: area of a circle..

#5 2009-12-04 21:57:41

Re: area of a circle..

#6 2009-12-05 22:24:37

Re: area of a circle..

#7 2009-12-05 22:31:31

Re: area of a circle..

#8 2009-12-12 17:36:11

Re: area of a circle..

#9 2009-12-12 17:37:12

Re: area of a circle..

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