# How To Use Law Of Cosines6 min read

The Law of Cosines is a trigonometric equation that is used to determine the length of a side of a triangle when two other sides and the angle between them are known. The equation is written as:

c^2 = a^2 + b^2 – 2ab cos(C)

where c is the length of the side opposite the angle C, a is the length of the side adjacent to angle C, and b is the length of the side opposite to angle A.

To use the Law of Cosines, you must first know the three sides of the triangle. You can then use the equation to calculate the length of the missing side.

For example, if you know that the length of side a is 5 and the length of side b is 6, and you want to find the length of side c, you would use the equation:

c^2 = a^2 + b^2 – 2ab cos(C)

c^2 = 25 + 36 – 2(5)(6) cos(C)

c^2 = 25 + 36 – 120 cos(C)

c^2 = -89

c = 9.6

Table of Contents

## How do you solve a triangle using the law of cosines?

There are various ways to solve a triangle, and the law of cosines is one of them. The law of cosines is used to find the third side of a triangle when two sides and the angle between them are known. To use the law of cosines, you need to know the cosine of the angle between the two known sides.

The law of cosines can be written as:

cos(A) = b^2 + c^2 – 2bc cos A

where A is the angle between the two known sides, b is the length of the side opposite the angle A, and c is the length of the side adjacent to the angle A.

To use the law of cosines to solve a triangle, you need to find the cosine of the angle between the two known sides. This can be done using a calculator or a trigonometric function table. Once you have the cosine of the angle, you can use the law of cosines to find the length of the third side of the triangle.

## How do you use law of sines and cosines?

The law of sines and cosines is a set of equations that can be used to solve for the angles and sides of a triangle. The law of sines can be used to solve for an angle in a triangle, while the law of cosines can be used to solve for a side in a triangle.

To use the law of sines, you first need to know the three angles of the triangle. You can then use the equation sin(A) = sin(B) / cos(B) to find the angle A. You can then use the equation sin(B) = sin(C) / cos(C) to find the angle B, and sin(C) = sin(D) / cos(D) to find the angle C.

To use the law of cosines, you first need to know the lengths of two of the sides of the triangle, and the angle between them. You can then use the equation c² = a² + b² – 2ab cos(C) to find the length of the third side.

## What are the 3 laws of cosine?

There are three fundamental laws of cosine, which are very important in trigonometry. They are:

The Law of Sines: This law states that the sine of an angle is equal to the ratio of the length of the opposite side to the length of the hypotenuse.

The Law of Cosines: This law states that the cosine of an angle is equal to the ratio of the length of the adjacent side to the length of the hypotenuse.

The Law of Tangents: This law states that the tangent of an angle is equal to the ratio of the length of the opposite side to the length of the adjacent side.

## How do you solve for cos?

To solve for cosine, you need to know the value of the angle and the length of the adjacent side. First, find the cosine of the angle by using the inverse cosine function on a calculator. Then, use the cosine equation to solve for the length of the adjacent side.

## How do you calculate cosine?

Cosine is a trigonometric function that is used to find the angles between two lines in a triangle. It is also used to find the length of the side adjacent to the angle. Cosine can be calculated using the following equation:

cosine = adjacent / hypotenuse

## How do you remember the cosine rule?

The cosine rule is a mathematical formula used to calculate the length of a side of a triangle, given the length of the other two sides. The rule is as follows:

a^2 = b^2 + c^2 – 2bc*cos(A)

where a, b, and c are the lengths of the sides of the triangle, and A is the angle between the two sides.

To remember the cosine rule, it can be helpful to think of it in terms of the Pythagorean theorem. The Pythagorean theorem states that the sum of the squares of the two shorter sides of a right triangle is equal to the square of the length of the longest side. In other words, a^2 + b^2 = c^2.

The cosine rule can be thought of as an extension of the Pythagorean theorem. In a right triangle, the longest side is the hypotenuse. The cosine rule states that the length of the hypotenuse is equal to the sum of the squares of the other two sides, minus the product of the two sides times the cosine of the angle between them. a^2 + b^2 = c^2 – 2bc*cos(A).

To use the cosine rule, you first need to calculate the cosine of the angle between the two sides. This can be done using a calculator, or by using the following formula:

cos(A) = (b*c – a*b*cos(B)) / (b*c)

where A is the angle between the two sides, b is the length of the side opposite the angle A, c is the length of the side adjacent to angle A, and B is the angle between the two sides opposite to side b.

Once you have calculated the cosine of the angle A, you can use the cosine rule to find the length of the hypotenuse. To do this, subtract the product of the two sides times the cosine of the angle between them from the square of the length of the longest side. a^2 + b^2 – 2bc*cos(A) = c^2.

## How do you know when to use sine cosine or tangent?

When it comes to using trigonometric functions, it’s important to know when to use sine, cosine, and tangent. Each of these functions can be used to solve different problems, but you need to know which one to use for the specific problem you’re trying to solve.

Sine is used to find the height of a triangle, cosine is used to find the length of a side of a triangle, and tangent is used to find the angle of a triangle. To use these functions, you need to know the lengths of the triangle’s sides and the angles between them.

If you’re not sure which function to use, try using a trigonometric calculator to help you out. This can be a helpful tool when you’re working on tricky problems.