ACT Math : Tetrahedrons

Study concepts, example questions & explanations for ACT Math

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Example Questions

Example Question #1 : How To Find The Volume Of A Tetrahedron

Find the volume of a regular tetrahedron if one of its edges is \(\displaystyle \sqrt[3]{6}\:cm\) long.

Possible Answers:

\(\displaystyle \frac{\sqrt2}{2}\;cm\)

\(\displaystyle 2\sqrt6\:cm\)

\(\displaystyle 2\sqrt3\:cm\)

\(\displaystyle \sqrt6\:cm\)

\(\displaystyle 4\sqrt3\:cm\)

Correct answer:

\(\displaystyle \frac{\sqrt2}{2}\;cm\)

Explanation:

Write the volume equation for a tetrahedron.

\(\displaystyle V=\frac{e^3}{6\sqrt2}\)

In this formula, \(\displaystyle V\) stands for the tetrahedron's volume and \(\displaystyle e\) stands for the length of one of its edges.

Substitute the given edge length and solve.

\(\displaystyle V=\frac{(\sqrt[3]6\:cm)^3}{6\sqrt2} = \frac{6\:cm^3}{6\sqrt2}= \frac{1}{\sqrt2}\:cm\)

Rationalize the denominator.

\(\displaystyle \frac{1}{\sqrt2}\:cm\cdot \frac{\sqrt2}{\sqrt2} = \frac{\sqrt2}{2}\:cm\)

Example Question #83 : Solid Geometry

Find the volume of a tetrahedron if the side length is \(\displaystyle \frac{1}{6}\).

Possible Answers:

\(\displaystyle \frac{\sqrt2}{1296}\)

\(\displaystyle \frac{\sqrt2}{16}\)

\(\displaystyle \frac{\sqrt2}{2592}\)

\(\displaystyle \frac{\sqrt2}{216}\)

\(\displaystyle \frac{3\sqrt2}{2}\)

Correct answer:

\(\displaystyle \frac{\sqrt2}{2592}\)

Explanation:

Write the equation to find the volume of a tetrahedron.

\(\displaystyle V=\frac{a^3}{6\sqrt2}\)

Substitute the side length and solve for the volume.

\(\displaystyle V=\frac{(\frac{1}{6})^3}{6\sqrt2}= \frac{1}{216}\left(\frac{1}{6\sqrt2}\right)= \frac{1}{1296\sqrt2}\)

Rationalize the denominator.

\(\displaystyle V=\frac{1}{1296\sqrt2} \cdot \frac{\sqrt2}{\sqrt2}= \frac{\sqrt2}{1296\cdot 2} = \frac{\sqrt2}{2592}\)

Example Question #1 : How To Find The Volume Of A Tetrahedron

What is the volume of a regular tetrahedron with an edge length of 6?

Possible Answers:

\(\displaystyle 24.2\)

\(\displaystyle 27.8\)

\(\displaystyle 26.6\)

\(\displaystyle 25.5\)

\(\displaystyle 32.1\)

Correct answer:

\(\displaystyle 25.5\)

Explanation:

The volume of a tetrahedron can be solved for by using the equation:

\(\displaystyle V= \frac{a^3}{6\sqrt{2}}\)

where \(\displaystyle a\) is the measurement of the edge of the tetrahedron. 

This problem can be quickly solved by substituting 6 in for \(\displaystyle a\)

\(\displaystyle V=\frac{6^3}{6\sqrt{2}}=\frac{216}{6\sqrt{2}}=\frac{36}{\sqrt{2}}\)

\(\displaystyle {\color{Blue} V=25.5}\)

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