2024 AMC 12A Problems/Problem 24
Problem
A 
is a tetrahedron whose triangular faces are congruent to one another. What is the least total surface area of a disphenoid whose faces are scalene triangles with integer side lengths?
Solution
Notice that any scalene acute triangle can be the faces of a . As a result, we simply have to find the smallest area a scalene acute triangle with integer side lengths can take on. This occurs with a 
triangle (notice that if you decrease the value of any of the sides the resulting triangle will either be isosceles, degenerate, or non-acute). For this triangle, the semiperimeter is 
, so by Heron’s Formula:
![\[A=\sqrt{\frac{15}{2}\cdot\frac{7}{2}\cdot\frac{5}{2}\cdot\frac{3}{2}}\]](http://latex.artofproblemsolving.com/d/c/8/dc83df1fb6076ad07fe018612746ae70c99008e1.png)
![\[=\sqrt{\frac{15^2\cdot7}{16}}\]](http://latex.artofproblemsolving.com/9/4/e/94ead419afd75655af08ac8d101786136566ffad.png)
![\[=\frac{15}{4}\sqrt{7}\]](http://latex.artofproblemsolving.com/d/b/0/db00938aa008ac6dce664c6272668e855bd741ae.png)
The surface area is simply four times the area of one of the triangles, or 
.
~eevee9406
See also
| 2024 AMC 12A (Problems • Answer Key • Resources) | |
| Preceded by Problem 23 |
Followed by Problem 25 |
| 1 • 2 • 3 • 4 • 5 • 6 • 7 • 8 • 9 • 10 • 11 • 12 • 13 • 14 • 15 • 16 • 17 • 18 • 19 • 20 • 21 • 22 • 23 • 24 • 25 | |
| All AMC 12 Problems and Solutions | |
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