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geometry senior
Problem
A trapezoid has side lengths 3, 5, 7, and 11. The sum of all the possible areas of the trapezoid can be written in the form of , where , , and are rational numbers and and are positive integers not divisible by the square of any prime. What is the greatest integer less than or equal to ?
(A)
(B)
(C)
(D)
Solution
Name the trapezoid , where is parallel to , , and . Draw a line through parallel to , crossing the side at . Then , . One needs to guarantee that , so there are only three possible trapezoids: In the first case, by Law of Cosines, , so . Therefore the area of this trapezoid is . In the second case, , so . Therefore the area of this trapezoid is . In the third case, , therefore the area of this trapezoid is . So , which rounds down to .
Final answer
D