# How to use law of cosines

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

To solve an SSS triangle: use The Law of Cosines first to calculate one of the angles. then use The Law of Cosines again to find another angle. and finally use angles of a triangle add to 180° to find the last angle.

In this triangle we know the three sides:

1. a = 8,
2. b = 6 and.
3. c = 7.

## Can you use law of cosines on right triangles?

You can ONLY use the Pythagorean Theorem when dealing with a right triangle. 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.

## 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.

## 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.

## What triangles do you use law of cosines for?

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.

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## Does law of sines work for any triangle?

The Law of Sines says that in any given triangle, the ratio of any side length to the sine of its opposite angle is the same for all three sides of the triangle. This is true for any triangle, not just right triangles.

## Does law of sines work for obtuse angles?

The sine rule is also valid for obtuse-angled triangles. = for a triangle in which angle A is obtus. We can use the extended definition of the trigonometric functions to find the sine and cosine of the angles 0°, 90°, 180°. Draw a diagram showing the point on the unit circle at each of the above angles.

## What is the law of sines and cosines?

The Law of Sines establishes a relationship between the angles and the side lengths of ΔABC: a/sin(A) = b/sin(B) = c/sin(C). Another important relationship between the side lengths and the angles of a triangle is expressed by the Law of Cosines. …

## Who discovered the law of sines and cosines?

Johannes von Muller

## 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).

## Is SSS law of cosines?

The Law of Cosines states that: Use the law of cosines when you are given SAS, or SSS, quantities. For example: If you were given the lengths of sides b and c, and the measure of angle A, this would be SAS. SSS is when we know the lengths of the three sides a, b, and c.

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## What is SSS SAS ASA AAS?

SSS (side-side-side) All three corresponding sides are congruent. SAS (side-angle-side) Two sides and the angle between them are congruent. ASA (angle-side-angle)