### How to Calculate the Sides and Angles of Triangles | Owlcation

Relationship between sides and angles. In any triangle, the largest side and largest angle are opposite one another. In any triangle, the smallest side and. How many degrees do the three angles of a triangle contain? They've got And that is the difference between an interior and an exterior angle. The easiest. In several geometries, a triangle has three vertices and three sides, where three angles of a The relation between angular defect and the triangle's area was first proven by Johann Heinrich Lambert. One can easily see how hyperbolic.

Now I'm going to go to the other two sides of my original triangle and extend them into lines. So I'm going to extend this one into a line. So, do that as neatly as I can. So I'm going to extend that into a line. And you see that this is clearly a transversal of these two parallel lines. Now if we have a transversal here of two parallel lines, then we must have some corresponding angles. And we see that this angle is formed when the transversal intersects the bottom orange line.

### Triangle Angle Sum Theorem ( Read ) | Geometry | CK Foundation

Well what's the corresponding angle when the transversal intersects this top blue line? What's the angle on the top right of the intersection?

Angle on the top right of the intersection must also be x. The other thing that pops out at you, is there's another vertical angle with x, another angle that must be equivalent. On the opposite side of this intersection, you have this angle right over here.

## Triangles Side and Angles

These two angles are vertical. So if this has measure x, then this one must have measure x as well.

Let's do the same thing with the last side of the triangle that we have not extended into a line yet. So let's do that. So if we take this one. So we just keep going. For this theorem, we only have two inequalities since we are just comparing an exterior angle to the two remote interior angles of a triangle. Let's take a look at what this theorem means in terms of the illustration we have below.

## How to Calculate the Sides and Angles of Triangles

By the Exterior Angle Inequality Theorem, we have the following two pieces of information: We will use this theorem again in a proof at the end of this section. Now, let's study some angle-side triangle relationships. Relationships of a Triangle The placement of a triangle's sides and angles is very important. We have worked with triangles extensively, but one important detail we have probably overlooked is the relationship between a triangle's sides and angles.

These angle-side relationships characterize all triangles, so it will be important to understand these relationships in order to enrich our knowledge of triangles. Angle-Side Relationships If one side of a triangle is longer than another side, then the angle opposite the longer side will have a greater degree measure than the angle opposite the shorter side. If one angle of a triangle has a greater degree measure than another angle, then the side opposite the greater angle will be longer than the side opposite the smaller angle.

In short, we just need to understand that the larger sides of a triangle lie opposite of larger angles, and that the smaller sides of a triangle lie opposite of smaller angles.

Let's look at the figures below to organize this concept pictorially. Since segment BC is the longest side, the angle opposite of this side,? A, is has the largest measure in? C, tells us that segment AB is the smallest side of? Now, we can work on some exercises to utilize our knowledge of the inequalities and relationships within a triangle.

Exercise 1 In the figure below, what range of length is possible for the third side, x, to be. When considering the side lengths of a triangle, we want to use the Triangle Inequality Theorem. Recall, that this theorem requires us to compare the length of one side of the triangle, with the sum of the other two sides.

The sum of the two sides should always be greater than the length of one side in order for the figure to be a triangle. Let's write our first inequality. So, we know that x must be greater than 3.

Let's see if our next inequality helps us narrow down the possible values of x. This inequality has shown us that the value of x can be no more than Let's work out our final inequality.

This final inequality does not help us narrow down our options because we were already aware of the fact that x had to be greater than 3. Moreover, side lengths of triangles cannot be negative, so we can disregard this inequality. Combining our first two inequalities yields So, using the Triangle Inequality Theorem shows us that x must have a length between 3 and Exercise 2 List the angles in order from least to greatest measure.

I know the lengths of all three sides SSS Use the cosine rule in reverse to work out each angle. Use the sine rule to work out the two unknown sides Summary of how to work out angles and sides of a triangle How Do You Measure Angles?

You can use a protractor or a digital angle finder.

**Exterior Angle Theorem For Triangles, Practice Problems - Geometry**

These are useful for DIY and construction if you need to measure an angle between two sides, or transfer the angle to another object. This tool comes in very handy when constructing stuff from wood or metal. I also use it as a replacement for a bevel gauge for transferring angles e. The rules are graduated in inches and centimetres and angles can be measured to 0.

The interior angles of all triangles add up to degrees. What Is the Hypotenuse of a Triangle? The hypotenuse of a triangle is its longest side.

What Do the Sides of a Triangle Add up to? The sum of the sides of a triangle depend on the individual lengths of each side. Unlike the interior angles of a triangle, which always add up to degrees How Do You Calculate the Area of a Triangle? To calculate the area of a triangle, simply use the formula: If you know two sides and the angle between them, use the cosine rule and plug in the values for the sides b, c, and the angle A.

Next, solve for side a.