Geometry
posted by al .
The circumference of a circle is 20 pi cm. Find diameter, radius, and area of the disk, the length of an arc of 90 angle and area of a 90 angle sector. Answer in terms of pi. d= ___ r= _____,
disk area= _______ arc length =______, sector area =________

Geometry 
Steve
90° is 1/4 of a circle. So, what's 1/4 of the circumference or area?
c = πd, so d = c/π
c = 2πr, so r = c/2π
a = πr^2 = π*(c/2π)^2 = c^2/4π
Now just plug in c where you need it.
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