Triangles

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ACT Math › Triangles

Questions 1 - 10
1

Find the perimeter of an equilateral triangle given side length of 2.

Explanation

To solve, simply multiply the side length by 3 since they are all equal. Thus,

2

What is the area of a triangle with a circle inscribed inside of it, in terms of the circle's radius R?

Circleinscribedintriangle

Explanation

Draw out 3 radii and 3 lines to the corners of each triangle, creating 6 30-60-90 triangles.

See that these 30-60-90 triangles can be used to find side length.

Formula for side of equilateral triangle is

.

Now substitute the new equation that is in terms of R in for S.

3

What is the area of a triangle inscribed in a circle, in terms of the radius R of the circle?

Triangleinscribedincircle2

Explanation

Draw 3 radii, and then 3 new lines that bisect the radii. You get six 30-60-90 triangles.

These triangles can be used ot find a side length .

Using the formula for the area of an equilateral triangle in terms of its side, we get

4

What is the hypotenuse of a right triangle with side lengths and ?

Explanation

The Pythagorean Theorem states that . This question gives us the values of and , and asks us to solve for .

Take and and plug them into the equation as and :

Now we can start solving for :

The length of the hypotenuse is .

5

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,

6

Find the perimeter of an equilateral triangle given side length of 2.

Explanation

To solve, simply multiply the side length by 3 since they are all equal. Thus,

7

Find the perimeter of an equilateral triangle whose side length is .

Explanation

To solve, simply multiply the side length by . Thus,

8

What is the area of a triangle inscribed in a circle, in terms of the radius R of the circle?

Triangleinscribedincircle2

Explanation

Draw 3 radii, and then 3 new lines that bisect the radii. You get six 30-60-90 triangles.

These triangles can be used ot find a side length .

Using the formula for the area of an equilateral triangle in terms of its side, we get

9

What is the area of a triangle with a circle inscribed inside of it, in terms of the circle's radius R?

Circleinscribedintriangle

Explanation

Draw out 3 radii and 3 lines to the corners of each triangle, creating 6 30-60-90 triangles.

See that these 30-60-90 triangles can be used to find side length.

Formula for side of equilateral triangle is

.

Now substitute the new equation that is in terms of R in for S.

10

_tri11

What is the value of in the triangle above? Round to the nearest hundredth.

Cannot be calculated

Explanation

Begin by filling in the missing angle for your triangle. Since a triangle has a total of degrees, you know that the missing angle is:

Draw out the figure:

_tri12

Now, to solve this, you will need some trigonometry. Use the Law of Sines to calculate the value:

Solving for , you get:

Rounding, this is .

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