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Geometry Difficulty 4.9 AIME Find the answer

Tetrahedron ABCDA B C D has side lengths AB=6,BD=62,BC=10,AC=8,CD=10A B=6, B D=6 \sqrt{2}, B C=10, A C=8, C D=10, and AD=6A D=6. The distance from vertex AA to face BCDB C D can be written as abc\frac{a \sqrt{b}}{c}, where a,b,ca, b, c are positive integers, bb is square-free, and gcd(a,c)=1\operatorname{gcd}(a, c)=1. Find 100a+10b+c100 a+10 b+c.

A number or a short expression. Spacing and $ signs are ignored.

Solution

First, we see that faces ABD,ABCA B D, A B C, and ACDA C D are all right triangles. Now, ABDA B D can be visualized as the base, and it can be seen that side ACA C is then the height of the tetrahedron, as ACA C should be perpendicular to both ABA B and ADA D. Therefore, the area of the base is 622=18\frac{6^{2}}{2}=18 and the volume of the tetrahedron is 1883=48\frac{18 \cdot 8}{3}=48. Now, let the height to BCDB C D be hh. The area of triangle BCDB C D comes out to 126282=641\frac{1}{2} \cdot 6 \sqrt{2} \cdot \sqrt{82}=6 \sqrt{41}. This means that the volume is 48=6h413=2h41h=2441=24414148=\frac{6 h \sqrt{41}}{3}=2 h \sqrt{41} \Longrightarrow h=\frac{24}{\sqrt{41}}=\frac{24 \sqrt{41}}{41}

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