reflex angle

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reflex angle

A student measures a reflex angle on a geometry worksheet.

Definition
  1. Noun:
    • An angle greater than 180 degrees but less than 360 degrees: A reflex angle is a type of angle that measures more than a straight angle (180°) but less than a full rotation (360°). It is the larger angle formed when two lines meet, representing the "outside" angle of a typical acute or obtuse angle.
Usage Examples
  • Noun:
    • In geometry, a reflex angle is always greater than 180 degrees.
    • To find the reflex angle, subtract the acute angle from 360 degrees.
    • The hands of a clock form a reflex angle at certain times, such as five minutes past one.
Advanced Usage

  • Identifying a reflex angle: In a diagram, a reflex angle is often the larger, exterior angle that is not usually marked. It is the complement to the smaller, interior angle at the same vertex that sums to 360°.

    • When given an angle of 70°, its corresponding reflex angle is 290° (360° - 70°).

  • "Greater than 180°": This is the defining characteristic. Any angle measurement falling strictly between 180 and 360 degrees is classified as a reflex angle.

    • An angle of 270 degrees is a classic example of a reflex angle.
Variants and Related Words
  • Angle (n): The general figure formed by two rays sharing a common endpoint (vertex).
  • Acute angle (n): An angle less than 90 degrees.
  • Obtuse angle (n): An angle greater than 90 degrees but less than 180 degrees.
  • Straight angle (n): An angle exactly equal to 180 degrees.
  • Full angle / Perigon (n): An angle exactly equal to 360 degrees.
Synonyms
  • None: In formal geometry, "reflex angle" is the specific, standard term for this measurement range. There are no direct synonyms, though it can be described as an "angle exceeding 180 degrees."
Related Phrases

  • "Measure of a reflex angle": The process of determining its degree value.

    • The measure of a reflex angle is always between 180 and 360.

  • "Interior and reflex angle pair": The two angles (one interior, typically less than 180°, and one reflex) that together form a full 360° rotation around a point.

    • The interior angle and its corresponding reflex angle are supplementary to 360 degrees.
Notes
  • Reflex angles are not as commonly depicted in basic geometry problems, which often focus on angles between 0° and 180°. They are important for understanding complete rotations and angular measurement in a full circle.
reflex angle

A student measures a reflex angle on a geometry worksheet.

Noun
  1. an angle greater than 180 degrees (but less than 360)