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Example Questions
Example Question #3 : Equilateral Triangles
One side of an equilateral triangle is equal to
Quantity A: The area of the triangle.
Quantity B:
The two quantities are equal.
Quantity B is greater.
Quantity A is greater.
The relationship cannot be determined.
Quantity B is greater.
To find the area of an equilateral triangle, notice that it can be divided into two
triangles:The ratio of sides in a
triangle is , and since the triangle is bisected such that the degree side is , the degree side, the height of the triangle, must have a length of .The formula for the area of the triangle is given as:
So the area of an equilateral triangle can be written in term of the lengths of its sides as:
For this particular triangle, since
, its area is equal to .
If the relation between ratios is hard to visualize, realize that
Example Question #6 : Equilateral Triangles
If the area of an equilateral triangle is
, what is the height of the triangle?
The area of an equilateral triangle is
.So let's set-up an equation to solve for
.Cross multiply.
The
cancels out and we get .Then take square root on both sides and we get
. To find height, we need to realize by drawing a height we create triangles.The height is opposite the angle
. We can set-up a proportion. Side opposite is and the side of equilateral triangle which is opposite is .Cross multiply.
Divide both sides by
We can simplify this by factoring out a
to get a final answer of .Example Question #95 : Geometry
Quantity A: The height of an equilateral triangle with an area of
Quantity B:
Which of the following is true?
Quantity B is greater.
The two quantities are equal.
The relationship cannot be determined.
Quantity A is greater.
Quantity B is greater.
This problem requires a bit of creative thinking (unless you have memorized the fact that an equilateral triangle always has an area equal to its side length times
.Consider the equilateral triangle:
Since this kind of triangle is a species of isoceles triangle, we know that we can drop down a height from the top vertex. This will create two equivalent triangles, one of which will look like:
This gives us a 30-60-90 triangle. We know that for such a triangle, the ratio of the side across from the 30-degree angle to the side across from the 60-degree angle is:
We can also say, given our figure, that the following equivalence must hold:
Solving for
, we get:
Now, since
, we know that must be smaller than . This means that or . Quantity B is larger than quantity A.Example Question #2 : How To Find The Height Of An Equilateral Triangle
Quantity A: The height of an equilateral triangle with perimeter of
.Quantity B:
Which of the following is true?
The two quantities are equal.
Quantity B is larger.
The relationship cannot be determined.
Quantity A is larger.
Quantity B is larger.
If the perimeter of our equilateral triangle is
, each of its sides must be or . This gives us the following figure:Since this kind of triangle is a species of isoceles triangle, we know that we can drop down a height from the top vertex. This will create two equivalent triangles, one of which will look like:
This gives us a 30-60-90 triangle. We know that for such a triangle, the ratio of the side across from the 30-degree angle to the side across from the 60-degree angle is:
Therefore, we can also say, given our figure, that the following equivalence must hold:
Solving for
, we get:
Now, since
, we know that must be smaller than . This means that orTherefore, quantity B is larger than quantity A.
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