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Classify angles into acute, right, obtuse, straight, and reflex based on their relationship to quarter and half turns.
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Defining straight and right angles.
Did you know? A book opened perfectly flat makes a straight line!
When the two arms of an angle lie perfectly flat, they form a straight angle. Think of it as a exact half turn around the vertex.
Defining angles smaller and larger than right/straight angles.
Once you know right (quarter turn) and straight (half turn) angles, you can easily classify the rest of the angle family based on their amount of rotation!
An angle that is smaller than a right angle is called an acute angle. It means "sharp," like the tip of a sharpened pencil or a slice of pizza. Its rotation is less than a quarter turn.
Matrix comparing all five angle types.
Visual examples of the 5 angle types.
Clean side-by-side comparison diagram showing five angle types: Acute with a small inner arc, Right with a square corner…
Match angle definitions to their names.
Terms
Definitions