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# Determination of Unknown Angles Using Law of Cosines

## Find unknown angle given lengths of all 3 sides

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Practice Determination of Unknown Angles Using Law of Cosines
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Oblique Triangles

#### Sides of an Oblique Triangle

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The included angle in a triangle is the angle between two known sides.

The law of cosines is a rule involving the sides of an oblique triangle stating that the square of a side of the triangle is equal to the sum of the squares of the other two sides plus two times the lengths of the other two sides times the cosine of the angle opposite the side being computed.

An oblique triangle is a triangle without a right angle as one of its internalangles.

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side angle side triangle is a triangle where two of the sides and the angle between them are known quantities.

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The Law of Cosines is one of the the equations used to solve a side or angle of an oblique triangle.

\begin{align*}c^2 = a^2 + b^2 - 2(a)(b)\cos C\end{align*}

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Remeber: The law of cosines only works if there are two sides and an angle present or if all three sides are present, if there is no SAS or SSS angle, the law of cosines cannot be used.

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Side Side Side Triangle: side side side triangle is a triangle where the lengths of all three sides are known quantities.

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