Volume

Geometry Level 2

The figure shown above is a regular pyramid with equilateral triangle as a base. Find the volume in cubic units rounded to the nearest whole number.


The answer is 37.

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1 solution

Solve for x x by cosine law,

6 2 = x 2 + x 2 2 ( x ) ( x ) c o s 6^2 = x^2 + x^2 - 2(x)(x) cos 120 120

x = 2 3 x = 2\sqrt{3}

Solve for h h by Pythagorean Theorem

h = 8 2 x 2 = 64 12 = 52 h = \sqrt{8^2 - x^2} = \sqrt{64 - 12} = \sqrt{52}

Solve for the area of the base,

A b = 1 2 ( 6 2 ) ( s i n A_{b} = \frac{1}{2}(6^2)(sin 60 ) = 18 60) = 18 s i n sin 60 60

Now solve for the volume,

V = 1 3 A b h = 1 3 ( 18 V = \frac{1}{3} A_{b}h = \frac{1}{3}(18 s i n sin 60 ) ( 52 ) = 37 60)(\sqrt{52}) = 37 c u b i c cubic u n i t s units

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