MathLabs

Problem 1

In a convex quadrilateral of area 3232, the sum of the lengths of two opposite sides and one diagonal is 1616. Determine all possible lengths of the other diagonal.
Step 7 of 7: Conclude and verify existence
In plain words

The answer is unique even though the quadrilateral itself has many shapes.

AC=82AC=8\sqrt2
Detailed analysis

Thus AC=82AC=8\sqrt2. Conversely, any AB,DC>0AB,DC>0 with AB+DC=8AB+DC=8, placed perpendicularly on opposite sides of an 88-segment BDBD, gives a convex quadrilateral of area 3232, so the value is attainable and unique.