Identify Angles and Lines
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Learning Objectives
- 1Identify and define acute, right, obtuse, and straight angles
- 2Classify angles by their size in degrees
- 3Identify parallel, perpendicular, and intersecting lines
- 4Recognize angles and lines in real-world shapes and objects
Mini Lesson
An angle is formed when two lines or rays meet at a point called the vertex. We measure angles in degrees (°). The size of an angle tells us how wide or narrow it is. Lines can also be classified by how they relate to each other — whether they meet, cross, or never touch.
Types of Angles
- Acute angle: less than 90° — a sharp, narrow angle.
- Right angle: exactly 90° — shown with a small square at the vertex.
- Obtuse angle: between 90° and 180° — a wide, blunt angle.
- Straight angle: exactly 180° — two rays pointing in opposite directions form a straight line.
- Reflex angle: greater than 180° (more than a half-turn).
Types of Lines
- Parallel lines: always the same distance apart; they never meet (written ||).
- Perpendicular lines: two lines that meet at exactly 90°.
- Intersecting lines: two lines that cross each other at any angle.
Tip: look for the right-angle square marker at a corner — that is always 90°. Acute means "sharp" and obtuse means "blunt" — use those clues to remember which is less than or greater than 90°.
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