The Concept of Angle in Trigonometry

 

In trigonometry, an angle is formed by two rays with the same initial point.

Let us study two rays: OK and OM, where OM is a moving ray that can rotate about point O.

Point O, relative to which the rotation takes place, is called the ‘center of rotation’ or a vertex.

OK is a fixed ray or the initial side of the angle;

ОМ is called a radius vector or the terminal side of the angle.

 

 

Determining the Angle of Rotation Using the Radius Vector

 

The angle of rotation is the value of rotation of the fixed radius vector relative to its initial position.

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O – vertex;

ОК — fixed ray or the initial side of the angle;

ОМ – radius vector or the terminal side of the angle.

∠КОМ — angle.

Radius vector OM can rotate

  • both in the positive direction (counterclockwise)
  • and in the negative direction (clockwise).

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Radius vector OM can rotate in the positive direction (counterclockwise)

 

 

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Radius vector OM can rotate in the negative direction (clockwise).