Definition: An angle is a way of measuring a part of a circle. Angles are measured in degrees with the symbol °. More

An angle marks off a section of a circle by extending two rays from the center of the circle.

  • The center of the circle is the vertex of the angle, the two rays are the legs of the angle.
  • If the two rays form a straight line, they divide the circle in half and the angle is 180°.
  • If the two rays mark off a quarter of a circle, the angle is 90° and is called a "right" angle.
  • Angles are also measured in radians (no unit) where 1 ≈ 57° and 180° = π ≈ 3.14 .

Interactivity

  • Click and drag the point С to change the angle <ABC .
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Regulations: Angle <ABC - basics

  • An angle of 90° is a fourth of a circle.
    • An angle of 90° is called a right angle.
    • An angle of 90° is marked by a square (make an angle of 90° in the interactivity below!).
  • An angle of 180° is a half of a circle.
    • An angle of 180° is the line segment \overline{CA} where the point B is the midpoint.
  • An angle of 360° is the whole circle.
    • An angle of 360° is the line segment \overline{BA} and the points А and С overlap.
    • An angle of 360° cannot be draw in the interactivity (it automatically reverts to the coterminal angle 0°).

Regulation: Angles in the coordinate plane and interactivity 2  

  • In the coordinate system, angles are measured counterclockwise starting from the positive x-axis.
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Page last modified on May 22, 2009, at 10:20 PM