Included Side
The side between two angles.
An included side is a side of a triangle that is included, or sandwiched, between two other sides. In other words, the included side is the side that is located between two other sides that meet at an angle, forming a vertex.
For example, in triangle ABC with sides AB, BC, and AC, if we have angle BAC, then the side AC is the included side because it is sandwiched between sides AB and BC at the vertex A.
Knowing that a side is an included side can be useful when solving triangles using trigonometry. For instance, if we know the length of one included side of a triangle and the measures of the two angles adjacent to it, we can use trigonometric functions such as sine, cosine, and tangent to find the lengths of the other sides and angles of the triangle.
It is important to note that when giving a description of a triangle, the included side is always described as being between the two other sides that meet at a common vertex.
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