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

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

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
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 .
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,
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,
Find the perimeter of an equilateral triangle whose side length is .
Explanation
To solve, simply multiply the side length by . Thus,
What is the area of a triangle inscribed in a circle, in terms of the radius R of the circle?

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

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.

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:

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 .