A point in a quadrilateral

Geometry Level 5

The figure above shows cyclic quadrilateral A B D C ABDC inscribed in circle O O , whose diagonals are congruent and share the same midpoint. A point E E is chosen, where E E is inside the quadrilateral. Let C E = 2 x + 1 CE=2x+1 , O D = 2 x + 10.5 OD=-2x+10.5 , and the circumference of the circle be 2 π x 2 8 π x + 15 π 2πx^2-8πx+15π . Also, B E : D B = 1 : 3 BE:DB = 1:3 . Determine the perimeter of triangle D E B DEB . Round your answer to the nearest thousandth. A scientific calculator is allowed.

Note: the figure is not to scale.

12.865 16.488 18.764 21.245

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1 solution

Yashas Ravi
May 14, 2018

The first step is to solve for x x , where 2 x + 10.5 = x 2 4 x + 7.5 -2x+10.5 = x^2 - 4x + 7.5 . The solutions are 1 -1 and 3 3 , but 1 -1 is negative, so 3 3 is the solution. After substituting the value 3 3 into ( 2 x + 1 ) (2x+1) for the length of C E CE , a system of equations can be formed using the Pythagorean Theorem relating B D BD , D C DC , and A D AD , Stewart's Theorem relating B D BD , A B AB , A E AE , E D ED , and B E BE , and the British Flag theorem relating C E CE , B E BE , A E AE , and E D ED . These equations can be used to determine B E BE , E D ED , and B D BD , where the values can be added to determine the perimeter of triangle B E D BED for a final answer of 18.764 18.764 .

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