Angles and Protractors Flashcards

Grade 4 · Math · Flashcards

Review angle types, measurements, and protractor skills with these study cards.

Flashcards

Angle: Formed by two rays sharing a common endpoint (vertex); measured in degrees (°)
Vertex: The point where two rays meet to form an angle; place the protractor's center hole here to measure
Degree (°): The unit used to measure angles; a full rotation = 360°, a half rotation = 180°, a quarter rotation = 90°
Acute angle: Greater than 0° and less than 90°; e.g., 45°, 72°
Right angle: Exactly 90°; marked with a small square symbol in diagrams
Obtuse angle: Greater than 90° and less than 180°; e.g., 110°, 155°
Straight angle: Exactly 180°; the two rays point in exactly opposite directions, forming a straight line
Reflex angle: Greater than 180° and less than 360°; the 'outside' angle going the long way around
Complementary angles: Two angles that add up to 90°; e.g., 40° and 50° are complementary
Supplementary angles: Two angles that add up to 180°; e.g., 120° and 60° are supplementary
Protractor steps: 1) Place center on vertex 2) Align one ray with 0° 3) Read degree where second ray crosses the same scale
Two scales on a protractor: Inner and outer scales run in opposite directions; always read from the 0° on the side your angle opens toward
Angle addition: If two adjacent angles share a ray, their measures add to give the whole angle; e.g., 40° + 65° = 105° total