# What is law of cosines

## What is the law of cosines used for?

The law of cosines allows us to find angle (or side length) measurements for triangles other than right triangles. The third side in the example given would ONLY = 15 if the angle between the two sides was 90 degrees. In the example in the video, the angle between the two sides is NOT 90 degrees; it’s 87.

## What is law of sines and cosines?

The Laws of Cosines and Sines. We saw in the section on oblique triangles that the law of cosines and the law of sines were useful in solving for parts of a triangle if certain other parts are known. … As usual, we’ll use a standard notation for the angles and sides of a triangle.

## How does law of cosine work?

The Law of Cosines is used to find the remaining parts of an oblique (non-right) triangle when either the lengths of two sides and the measure of the included angle is known (SAS) or the lengths of the three sides (SSS) are known. The Law of Cosines states: … c2=a2+b2−2ab cosC .

## Can law of cosines be used on any triangle?

In this case the tool is useful when you know two sides and their included angle. From that, you can use the Law of Cosines to find the third side. It works on any triangle, not just right triangles. where a and b are the two given sides, C is their included angle, and c is the unknown third side.

## How do you use the law of cosines?

The cosine rule is used when we are given either a) three sides or b) two sides and the included angle.

1. The sine rule. Study the triangle ABC shown below. Let B stands for the angle at B. Let C stand for the angle at C and so on. …
2. The cosine rule. Refer to the triangle shown below. b = AC. c = AB.
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## What is the rule of sin?

Sine Rule. The Sine Rule can be used in any triangle (not just right-angled triangles) where a side and its opposite angle are known. You will only ever need two parts of the Sine Rule formula, not all three. You will need to know at least one pair of a side with its opposite angle to use the Sine Rule.

## Where is angle of depression?

The angle of depression is the angle between the horizontal line of sight and the line of sight down to an object. For example, if you were standing on top of a hill or a building, looking down at an object, you could measure the angle of depression.

## Why does the law of sines work?

The Law of Sines is the relationship between the sides and angles of non-right (oblique) triangles . Simply, it states that the ratio of the length of a side of a triangle to the sine of the angle opposite that side is the same for all sides and angles in a given triangle.

## How is the law of cosines proven?

The Law of Cosines is a theorem which relates the side-lengths and angles of a triangle. It can be derived in several different ways, the most common of which are listed in the “proofs” section below. It can be used to derive the third side given two sides and the included angle.

## How do you solve SSS law of cosines?

To solve an SSS triangle:

1. use The Law of Cosines first to calculate one of the angles.
2. then use The Law of Cosines again to find another angle.
3. and finally use angles of a triangle add to 180° to find the last angle.
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## What does Sine mean?

In mathematics, the sine is a trigonometric function of an angle. The sine of an acute angle is defined in the context of a right triangle: for the specified angle, it is the ratio of the length of the side that is opposite that angle, to the length of the longest side of the triangle (the hypotenuse).