# Sides and angles of a triangle relationship theory

### The relations of the sides and angles of a triangle. Euclid I. 18,

The two legs meet at a 90° angle and the hypotenuse is the longest side of the The Pythagorean Theorem tells us that the relationship in every right triangle is. Solution of triangles (Latin: solutio triangulorum) is the main trigonometric problem of finding If only the angles are given, the side lengths cannot be determined, because any similar triangle is a solution. .. Among other relationships that may be useful are the half-side formula and Napier's analogies: tan c 2 cos α − β. Recall that in a scalene triangle, all the sides have different lengths and all the interior angles have different measures. In such a triangle, the shortest side is.

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. Then use the angle value and the sine rule to solve for angle B. Finally, use your knowledge that the angles of all triangles add up to degrees to find angle C.

Assuming the triangle is right, use the Pythagorean theorem to find the missing side of a triangle. The formula is as follows: A triangle with two equal sides and one side that is longer or shorter than the others is called an isosceles triangle.

What Is the Cosine Formula? This formula gives the square on a side opposite an angle, knowing the angle between the other two known sides. For a triangle, with sides a,b and c and angles A, B and C the three formulas are: Since a triangle is a plane and two-dimensional object, it is impossible to discover its volume. A triangle is flat. 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. 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.

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.

- Triangles Side and Angles
- The Pythagorean Theorem
- Isosceles Triangle

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.

### Isosceles Triangle -- from Wolfram MathWorld

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.

## Geometry: Triangle Inequality and Angle-Side Relationship

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.

## THE SIDES AND ANGLES OF A TRIANGLE

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.

**Angle side relationship**

For this exercise, we want to use the information we know about angle-side relationships. Since all side lengths have been given to us, we just need to order them in order from least to greatest, and then look at the angles opposite those sides.