# Dakota's travel toothbrush case, shaped like an equilateral triangular prism, has perpendicular height of 2.3 in. and depth of 8.4 in. How much plastic is the case made out of, in sq. in.?

##### 1 Answer

About

#### Explanation:

Assuming this includes plastic to cover the three long sides as well as the two triangular ends, Let's look at the ends first:

The perpendicular height of the triangle is an altitude drawn from the top vertex, which gives you two 30-60-90 triangles on either end.

On questions like this, *always draw a picture first!!*

You can use the law of sines to set it up like this:

Or you can use your 30-60-90 rules, which say that the long leg (the perpendicular height) is

Either method gives you a value where

To find the area of the triangles, use the formula

For the long sides, you just have three congruent rectangles. Taking that value of

Three of these plus the two triangles on the end, the surface area is about