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geometry senior
Problem
The total area of all the faces of a rectangular solid is , and the total length of all its edges is . Then the length in cm of any one of its interior diagonals is
(A)
(B)
(C)
(D)
Solution
Let the edge lengths be , and . Therefore, the total area of all its faces is . Therefore, and . Also, the total lengths of all of its edges is , so , and . Therefore, we have: and . The length of the interior diagonal is , so if we can find , we can find the diagonal. We square the second equation above to introduce an : . However, we already know that , so .
Final answer
D