basic definitions in geometry

Basic Definitions in Geometry

Acute Angle

• An angle that measures between 0 and 90 degrees.

Right Angle

• Angle that measures 90 degrees and formed by perpendicular lines.

Obtuse Angle

• An angle that measures between 90 and 180 degrees.

Straight Angle

• An angle that measures 180 degrees.

Reflex Angle

• An angle that measures between 180 and 360 degrees.

Complementary Angle

• Two angles that add up to 90 degrees.

Supplementary Angles

• Two angles that add up to 180 degrees.

Equilateral Triangle

• A triangle that has 3 equal sides.

Equiangular Triangle

• A triangle that has 3 equal angles and each measures 60 degrees (sum is 180).

Scalene Triangle

• Triangle with different sides and angles.

Isosceles Triangle

• A triangle that has two equal sides and two equal base angles.

Vertical Angles

• Two angles in which the sides of one angle are opposite rays to the sides of the second angle.

Adjacent Angles

• Two angles having a common vertex and a common side, but do not have any interior points in common.

Line Segment

• 2 points called endpoints and all of the points in between them.

Ray

• A part of a line that consists of a point on the line, called the endpoint, and all of the points on one side of the line.

Opposite Rays

• Two rays of the same line with a common endpoint and no other points in common.

Collinear

• A set of points all lying on the same straight line.

Midpoint

• The point of a line segment that divides it into 2 congruent (equal) parts.

Bisector

• A line, ray, or segment which divides a segment into 2 congruent parts.

Perpendicular Lines

• Two lines that intersect to form right angles.

Altitude

• The perpendicular segment from a vertex of a polygon to the opposite side.

Median

• A segment that joins any vertex of a triangle to the midpoint of the opposite side.