Homework Help: maths-urgently

Posted by Anonymous on Sunday, January 20, 2013 at 4:36am.

An arc of a circle is of length 5p cm and the sector is bounds has an area of
20p cm^2
find the radius of the circle.

maths-urgently - Reiny, Sunday, January 20, 2013 at 8:50am
let the radius be r
circumference = 2πr
area = πr^2

πr^2/20π = 2πr/5π
r^2/20 = 2r/5
5r^2 = 40r
r^2 - 8r = 0
r(r-8) = 0
r = 8 or r = 0, of course we would want r > 0 to any area at all

r = 8

check:
if r = 8
circumf= 16π
area= 64π

20π/64π = 5/16
5π/16π = 5/16
All looks good
maths-urgently - Anonymous, Sunday, January 20, 2013 at 8:59am
thank u @reiny

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