SOLUTION: A quadrilateral contains an inscribed circle. The ratio of the perimeter of the quadrilateral to that of the circle is 4:3. Find the ratio of the area of the quadrilateral to that

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Question 1018212: A quadrilateral contains an inscribed circle. The ratio of the perimeter of the quadrilateral to that of the circle is 4:3. Find the ratio of the area of the quadrilateral to that of the circle.
Answer by ikleyn(52866) About Me  (Show Source):
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A quadrilateral contains an inscribed circle. The ratio of the perimeter of the quadrilateral to that of the circle is 4:3.
Find the ratio of the area of the quadrilateral to that of the circle.
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If a quadrilateral has/contains an inscribed circle, then the area of the quadrilateral is 


S%5Bq%5D = %28P%2F2%29%2Ar,


where P is the quadrilateral's perimeter, and r is the radius of the inscribed circle.

It is well known fact. See the lesson Area of a quadrilateral circumscribed about a circle in this site. 

From the other side, the circumference of the circle is S = 2%2Api%2Ar, and the area of the circle S is S = pi%2Ar%5E2.

Therefore,

S%5Bq%5D%2FS = %28P%2F2%29%2Ar : pi%2Ar%5E2 = P%2F%282%2Api%2Ar%29.

Now recall that  P%2F%282%2Api%2Ar%29 = 4%2F3,  it is given.

Hence,  S%5Bq%5D%2FS = 4%2F3.

The solution is complete.