45/45/90 Right Isosceles Triangles

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ACT Math › 45/45/90 Right Isosceles Triangles

Questions 1 - 10
1

Find the hypotenuse of an isosceles right triangle given side length of 3.

Explanation

To solve, simply use the Pythagorean Theorem.

Recall that an isosceles right triangle has two leg lengths that are equal.

Therefore, to solve for the hypotenuse let and in the Pythagorean Theorem.

Thus,

2

Find the hypotenuse of an isosceles right triangle given side length of 3.

Explanation

To solve, simply use the Pythagorean Theorem.

Recall that an isosceles right triangle has two leg lengths that are equal.

Therefore, to solve for the hypotenuse let and in the Pythagorean Theorem.

Thus,

3

What is the area of an isosceles right triangle with a hypotenuse of ?

Explanation

Now, this is really your standard triangle. Since it is a right triangle, you know that you have at least one -degree angle. The other two angles must each be degrees, because the triangle is isosceles.

Based on the description of your triangle, you can draw the following figure:

_tri101

This is derived from your reference triangle for the triangle:

Triangle454590

For our triangle, we could call one of the legs . We know, then:

Thus, .

The area of your triangle is:

For your data, this is:

4

What is the perimeter of an isosceles right triangle with an hypotenuse of length ?

Explanation

Your right triangle is a triangle. It thus looks like this:

_tri41

Now, you know that you also have a reference triangle for triangles. This is:

Triangle454590

This means that you can set up a ratio to find . It would be:

Your triangle thus could be drawn like this:

_tri42

Now, notice that you can rationalize the denominator of :

Thus, the perimeter of your figure is:

5

What is the area of an isosceles right triangle with a hypotenuse of ?

Explanation

Now, this is really your standard triangle. Since it is a right triangle, you know that you have at least one -degree angle. The other two angles must each be degrees, because the triangle is isosceles.

Based on the description of your triangle, you can draw the following figure:

_tri101

This is derived from your reference triangle for the triangle:

Triangle454590

For our triangle, we could call one of the legs . We know, then:

Thus, .

The area of your triangle is:

For your data, this is:

6

What is the perimeter of an isosceles right triangle with an hypotenuse of length ?

Explanation

Your right triangle is a triangle. It thus looks like this:

_tri41

Now, you know that you also have a reference triangle for triangles. This is:

Triangle454590

This means that you can set up a ratio to find . It would be:

Your triangle thus could be drawn like this:

_tri42

Now, notice that you can rationalize the denominator of :

Thus, the perimeter of your figure is:

7

What is the perimeter of an isosceles right triangle with an area of ?

Explanation

Recall that an isosceles right triangle is also a triangle. Your reference figure for such a shape is:

Triangle454590 or _tri51

Now, you know that the area of a triangle is:

For this triangle, though, the base and height are the same. So it is:

Now, we have to be careful, given that our area contains . Let's use , for "side length":

Thus, . Now based on the reference figure above, you can easily see that your triangle is:

_tri71

Therefore, your perimeter is:

8

What is the perimeter of an isosceles right triangle with an area of ?

Explanation

Recall that an isosceles right triangle is also a triangle. Your reference figure for such a shape is:

Triangle454590 or _tri51

Now, you know that the area of a triangle is:

For this triangle, though, the base and height are the same. So it is:

Now, we have to be careful, given that our area contains . Let's use , for "side length":

Thus, . Now based on the reference figure above, you can easily see that your triangle is:

_tri71

Therefore, your perimeter is:

9

A tree is feet tall and is planted in the center of a circular bed with a radius of feet. If you want to stabalize the tree with ropes going from its midpoint to the border of the bed, how long will each rope measure?

Explanation

This is a right triangle where the rope is the hypotenuse. One leg is the radius of the circle, 5 feet. The other leg is half of the tree's height, 12 feet. We can now use the Pythagorean Theorem giving us . If then .

10

The height of a triangle is . What is the length of the hypotenuse?

Explanation

Remember that this is a special right triangle where the ratio of the sides is:

In this case that makes it:

Where is the length of the hypotenuse.

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