Geometry Vocabulary Introduction to Classifying Angles

Line a straight path that connects two points, but extends past both points, forever. to identify a line, select two points, and draw the symbol of a line over it. A line ALWAYS has arrows at both ends.

Segment two points and all the points in a straight path between them to identify a segment, select two endpoints, and draw the symbol of a segment over it. A segment DOES NOT have arrows at the ends.

Ray an endpoint and all the points in a straight path in one direction to identify a ray, start with an endpoint, then use another point in the direction you want. For example, point G going to point B would be:

Vertex the common endpoint of an angle. (also, a corner point of a geometric figure) How do you recognize a vertex?

Angle two rays with a common endpoint. How do you name an angle?

Right Angle an angle that measures exactly 90° How do you identify a right angle?

Acute Angle an angle that measures less than 90° What does it look like?

Straight Angle an angle that measures exactly 180° What does it look like?

Obtuse Angle an angle that measures more than 90°, AND less than 180° What two angles is an obtuse angle between?

Adjacent Angles two angles that share a common vertex, and one side, but have no common interior points. How would you draw adjacent angles?

Vertical Angles when 2 lines intersect, they form 4 angles. The angles across from each other are called, ‘vertical angles.’ What do vertical angles look like?

Complementary Angles the sum of their measures equals 90° What kind of angle do complementary angles form?

Supplementary Angles the sum of their measures equals 180° What kind of angle do supplementary angles form?

Triangles & more vocabulary

Triangle a polygon with three sides. The sum of the 3 angles equals exactly 180°.

Congruent being exactly equal in size and shape. What can be congruent? sides angles polygon

Scalene Triangle has NO congruent sides.

Isosceles Triangle has at least TWO congruent sides.

Equilateral Triangle has THREE congruent sides. Question: If the three sides are congruent, what do you think each angle measure will be? 60°

Right Triangle a triangle with a right angle If one angle is 90°, what must be the sum of the other two angles?

Acute Triangle a triangle with ALL three angles being acute angles.

Obtuse Triangle A triangle with one obtuse angle. If a triangle is obtuse, what type of angles must the other two angles be?