How To Name An Angle 11 Steps With Pictures

For example, you might have an angle with a vertex at point C.

For example, on the top ray of the angle, you might have point A. On the bottom ray of the angle, you might have point B.

For example, an angle with a vertex C, and a point A on the top ray, and the point B on the bottom ray, would be labeled ∠ACB{\displaystyle \angle ACB}.

For example, ∠DEF{\displaystyle \angle DEF} measures 40 degrees. Since 40 is less than 90, it is an acute angle.

For example, ∠IHJ{\displaystyle \angle IHJ} measures 125 degrees. Since 125 is between 90 and 180, it is an obtuse angle.

Note that 180 is half of 360, which is the measurement of a complete turn, or circle. So a straight angle is an angle that is open exactly halfway.

Think of an angle opening to a complete rotation. When it is open half way, it is a straight angle. If the angle opens beyond that, it is a reflex angle. Take, for example, a right angle. A right angle really makes two angles. One is the 90 degree angle inside the square corner. However, if you think of the angle opening the opposite way, you can see that it could also makes a 270 degree angle.

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