2014
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Learn how to use the cosine rule to find the third side or the angles of a triangle when you know two sides and the angle between them. See examples, formulas, and tips to remember the law of cosines.
- The Law of Sines
And it says that: When we divide side a by the sine of angle...
- Solving Triangles
In this case, we have no choice. We must use The Law of...
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About Ads - The Law of Cosines - Math is Fun
- The Law of Sines
The law of cosines states that for an arbitrary triangle with sides a, b, and c and angles opposite those sides A, B and C: a 2 + b 2 − 2 a b cos ( C ) = c 2 {\displaystyle a^{2}+b^{2}-2ab\cos(C)=c^{2}}
The angles α (or A ), β (or B ), and γ (or C) are respectively opposite the sides a, b, and c. In trigonometry, the law of cosines (also known as the cosine formula or cosine rule) relates the lengths of the sides of a triangle to the cosine of one of its angles.
Learn what cosine is, how to find its values using right triangles or unit circle, and how to use a calculator or a table. See commonly used angles and their cosine values, and how to use reference angles to extend the domain of cosine.
Learn how to use the law of cosines to find the missing side or angle of a triangle given the known elements. The law of cosines relates the lengths of the sides of a triangle to the cosine of one of its angles and generalizes the Pythagoras theorem.
Learn about the cosine function, one of the three main trigonometric functions, and its properties, graph, inverse, identities, and calculus. Find cosine values, formulas, tables, worksheets, and examples for class 10 and 12 maths.
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.
- 5 min
- Sal Khan
