Question 328749
{{{drawing(300,300,-10,10,-10,10,circle(0,0,.3),line(0,0,-7.8,4.5),locate(-1,3,6),locate(4.8,2.5,24),locate(.2,1.5,C),locate(3,6,b),line(-7.8,4.5,7.8,4.5),blue(line(0,0,0,4.5)),line(0,0,7.8,4.5),circle(0,0,9))}}}
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The area of the entire pie slice is equal to the area of the two triangle plus the remaining portion. 
I'm not sure which area you require.
You can calculate the entire pie slice area by finding the angle C. 
You can calculate the two triangles area by finding b. 
Let's find {{{b}}} first. 
From the diagram above,
{{{6^2+b^2=12^2}}}
{{{b^2=144-36}}}
{{{b=sqrt(108)}}}
{{{b=6sqrt(3)}}}
So then the area of the triangle is,
{{{At=(1/2)(6)(6sqrt(3))=18sqrt(3)}}}
You can calculate the angle C using trigonometry.
{{{cos(C)=6/12=0.5}}}
{{{C=pi/3}}}
For the entire circle, the area is {{{Ac=pi(12)^2}}}
Since we only have a {{{2C}}} slice out of {{{2pi}}}, then the area of the slice is 
{{{As=((2pi/3)/(2pi))*pi*12^2}}}
{{{As=(144/3)pi}}}
{{{As=48pi}}}
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So now we have all of the pieces.
{{{As=2At+Ar}}}
where Ar is the area of the remaining portion. 
{{{48pi=2(18sqrt(3))+Ar}}}
{{{Ar=48pi-36sqrt(3)}}}