in a circle with perimeter of 20cm a sector has radius r, angle θ radians and area Acm^2(adsbygoogle = window.adsbygoogle || []).push({});

prove that A= 25-(r-5)^2

A=1/2 r^2 θ

c=2Πr

the only thing that I can think to do is c=2Πr therefore 20=2Πr

10=Πr r=10/Π

so then A=1/2 r^2 θ

=1/2 (10/Π)^2 θ

= θ (100/2Π^2)

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# Homework Help: Proving area with radians

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