# Relationship between angles and sides

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

If you work out the angles using elementary trigonometry you find . For instance, if you extend side AB such that the new position of corner B (call it B. This concept teaches students the relationship between opposite angles and sides in triangles and how to use this relationship to compare. 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.

In this section, we will learn about the inequalities and relationships within a triangle that reveal information about triangle sides and angles. First, let's take a look at two significant inequalities that characterize triangles.

Inequalities of a Triangle Recall that an inequality is a mathematical expression about the relative size or order of two objects. In geometrywe see the use of inequalities when we speak about the length of a triangle's sides, or the measure of a triangle's angles.

- Inequalities and Relationships Within a Triangle
- Solution of triangles
- The Pythagorean Theorem

Let's begin our study of the inequalities of a triangle by looking at the Triangle Inequality Theorem. Triangle Inequality Theorem The sum of the lengths of two sides of a triangle must always be greater than the length of the third side. Let's take a look at what this theorem means in terms of the triangle we have below.

The Triangle Inequality Theorem yields three inequalities: Since all of the inequalities are satisfied in the figure, we know those three side lengths can form to create a triangle. It is important to understand that each inequality must be satisfied. If for some reason, a triangle were to have one side whose length was greater than the sum of the other two sides, we would have a triangle that has a segment that is either too short so that the triangle is not closedor too long so that a side of the triangle extends too far.

All of our inequalities are not satisfied in the diagram above. The original illustration shows an open figure as a result of the shortness of segment HG.

Now, we will look at an inequality that involves exterior angles. Exterior Angle Inequality Theorem The measure of an exterior angle of a triangle is greater than the measure of either of its remote interior angles. 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. 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? Thus, it has no volume. Triangular prisms, on the other hand, are three-dimensional objects with a determinable volume.

To determine the volume of a triangular prism, you must discover the area of the base of the prism, then multiply it by the height. You need to know at least one side, otherwise you can't work out the lengths of the triangle. There's no unique triangle that has all angles the same. Triangles with the same angles are similar but the ratio of sides for any two triangles is the same.

Use the cosine rule in reverse. The cosine rule states: Source You can measure an angle with a digital angle finder.

Source Triangles in the Real World A triangle is the most basic polygon and can't be pushed out of shape easily, unlike a square. If you look closely, triangles are used in the designs of many machines and structures because the shape is so strong.

**Angle side relationship**

The strength of the triangle lies in the fact that when any of the corners are carrying weight, the side opposite acts as a tie, undergoing tension and preventing the framework from deforming. For example, on a roof truss the horizontal ties provide strength and prevent the roof from spreading out at the eaves.

## Ordering triangle sides and angles example

The sides of a triangle can also act as struts, but in this case they undergo compression. An example is a shelf bracket or the struts on the underside of an airplane wing or the tail wing itself. Click thumbnail to view full-size Truss bridge. So, how are we supposed to actually order them from shortest to longest?

### geometry - Relation between angles and sides of an Isosceles triangle - Mathematics Stack Exchange

Well, the realization that you need to make here is that the order of the lengths of the sides of a triangle are related to the order of the measures of angles that open up onto those sides. What do I mean by that? Well, let's think about these three angles right over here. So, b is going to be the shortest side. So, the next largest angle is 58 degrees, and so a is going to be the middle side. It's not going to be the longest nor the shortest.

Then 65 degrees, that opens up onto side c, or the opposite side of that angle is c. So, c is going to be the longest side. To get an intuition for why that is, imagine a world where the 65 degree angle, if we were to make it bigger.