DEFINITIONS YOU NEED TO KNOW FOR MATH 221

• a segment
• a ray
• opposite rays
• an angle
• supplementary angles
• a right angle
• two lines are parallel

• the midpoint of a segment
• the perpendicular bisector of a segment
• three points are collinear
• three lines are concurrent
• a triangle (includes vertices, sides, angles, sides adjacent/opposite to a vertex)
• an isosceles triangle
• an equilateral triangle
• a right triangle

• a rectangle

• a projective plane
• an affine plane

• two points are on the same side (opposite sides) of a line
• a side of a line
• the interior of an angle
• a ray is between two other rays
• the interior/exterior of a triangle

• two triangles are congruent
• AB < CD
• angle(ABC) < angle(DEF)

• a transversal
• alternate interior angles
• an exterior angle of a triangle
• remote interior angles of a triangle
• the bisector of an angle

• the angle sum of a triangle
• the defect of a triangle
• two triangles are similar

• A Saccheri quadrilateral
• A Lambert quadrilateral

• A limiting parallel ray
• the angle of parallelism at a point relative to a line
• asymptotically parallel lines
• divergently parallel lines