# When to use the law of sines

## How do you know when to use the law of sines or cosines?

The sine rule is used when we are given either a) two angles and one side, or b) two sides and a non-included angle. The cosine rule is used when we are given either a) three sides or b) two sides and the included angle.

## When would you use the law of sines to solve a triangle?

The law of sines is used to solve triangles in which you know only two angles and one of the opposing sides (called AAS for angle-angle-side), or two sides and one of the opposing angles (called SSA for side-side-angle).

## Why does the law of sines not always work?

Cases when you can not use the Law of Sines

Since we do not know an opposite side and angle, we cannot employ the formula. Or, just look at it: Remember when you have 2 sides, the angle must be non-included. By the way, we could use the law of cosines to find the length of the side opposite the 115° angle.

## Can you use the law of sines on a right 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. Press ‘reset’ in the diagram above.

## 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.

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## How do you use the law of cosines?

When to Use

The Law of Cosines is useful for finding: the third side of a triangle when we know two sides and the angle between them (like the example above) the angles of a triangle when we know all three sides (as in the following example)

## 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.

## How do you prove the law of sines?

Another way of stating the Law of Sines is: The sides of a triangle are proportional to the sines of their opposite angles. To prove the Law of Sines, let △ABC be an oblique triangle. Then ∠ABC can be acute, as in Figure 2.1. 1(a), or it can be obtuse, as in Figure 2.1.

## 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.

## How do you tell if it’s an ambiguous case?

Explanation:

1. If angle A is acute, and a
2. If angle A is acute, and a = h, one possible triangle exists.
3. If angle A is acute, and a > b, one possible triangle exists.
4. If angle A is acute, and h

## How do you do the law of sines step by step?

How to Use the Law of Sines with a Triangle

1. Using the law of sines and the proportion.
2. fill in the values that you know. Use the given values, not those that you’ve determined yourself. …
3. Use a calculator to determine the values of the sines (in this case, rounded to three decimal places).
4. Multiply each side by the denominator under b to solve for that length.

## How do you calculate sine?

In any right triangle, the sine of an angle x is the length of the opposite side (O) divided by the length of the hypotenuse (H). In a formula, it is written as ‘sin’ without the ‘e’:

## Do all triangles equal 180?

In a Euclidean space, the sum of angles of a triangle equals the straight angle (180 degrees, π radians, two right angles, or a half-turn). … It was unknown for a long time whether other geometries exist, for which this sum is different.