Is Triangle ABC a Right-Angled Triangle in Tetrahedron OABC?

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In summary, a right-angled triangle is a triangle with one angle measuring exactly 90 degrees, while a tetrahedron is a three-dimensional polyhedron with four triangular faces. To determine if a triangle is right-angled in a tetrahedron, the Pythagorean theorem can be used. There is a relationship between a right-angled triangle and a tetrahedron, as four right-angled triangles are formed within the tetrahedron. It is also possible for a triangle to become right-angled in a tetrahedron even if it was not right-angled in its original position.
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Ackbach
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Happy New Year! Here is this year's first University-level POTW:

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Tetrahedron $OABC$ is such that lines $OA, OB,$ and $OC$ are mutually perpendicular. Prove that triangle $ABC$ is not a right-angled triangle.

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Remember to read the http://www.mathhelpboards.com/showthread.php?772-Problem-of-the-Week-%28POTW%29-Procedure-and-Guidelines to find out how to http://www.mathhelpboards.com/forms.php?do=form&fid=2!
 
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Congratulations to Opalg and castor28 for their correct solutions to this week's POTW, which was Problem 63 in the MAA Challenges. castor28's solution follows:

[sp]We can take an orthogonal coordinate system with $O$ as origin and one axis through each of $A, B,$ and $C$. The coordinates of the vertices are $A = (a, 0, 0), \; B=(0,b,0),$ and $C=(0,0,c)$.

We compute the dot product of the vectors $AB$ and $AC$:
$$ AB\cdot AC = (-a,b,0)\cdot(-a,0,c) = a^2\ne 0.$$

This shows that $\angle BAC$ is not a right angle; the same argument applies to the other two angles of the triangle $ABC$.
[/sp]
 

FAQ: Is Triangle ABC a Right-Angled Triangle in Tetrahedron OABC?

1. What is a right-angled triangle?

A right-angled triangle is a triangle with one angle measuring exactly 90 degrees, also known as a right angle. In a right-angled triangle, the side opposite the right angle is called the hypotenuse.

2. What is a tetrahedron?

A tetrahedron is a three-dimensional polyhedron with four triangular faces. It is a type of pyramid with a triangular base and three triangular faces that meet at a single point, called the apex.

3. How can you determine if a triangle is right-angled in a tetrahedron?

In order to determine if a triangle is right-angled in a tetrahedron, you can use the Pythagorean theorem. If the square of the length of one side of the triangle is equal to the sum of the squares of the other two sides, then the triangle is right-angled.

4. What is the relationship between a right-angled triangle and a tetrahedron?

In a tetrahedron, there are four right-angled triangles formed by connecting the three vertices of the base triangle to the apex. These right-angled triangles are important in determining the overall structure and dimensions of the tetrahedron.

5. Can a triangle be right-angled in a tetrahedron if it is not right-angled in its original position?

Yes, it is possible for a triangle to become right-angled in a tetrahedron even if it was not right-angled in its original position. This can happen if the triangle is rotated or positioned in a certain way within the tetrahedron.

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