Geometry: Vocabulary

A point can be described as a location in space. Represented by a dot and is named by writing a capital letter next to the dot. POINT A line is a straight row of points that goes on forever in both directions. A line is drawn by using arrow heads at both ends. LINE A line segment is a piece of a line that has two endpoints. A line segment is named for its endpoints. The segment with endpoints A and B shown to the right is named: LINE SEGMENT A ray is a part of a line that has only one endpoint and goes on forever in one direction. A ray is named by using the endpoint and some other point on the ray: RAY Lines that are on the same plane, but that never intersect (cross). PARALLEL LINES Lines that intersect (cross). INTERSECTING LINES An angle is made up of two rays that start at a common endpoint. The common endpoint is called the vertex. Named: ANGLE Angles can be measured in degrees. The symbol for degrees is a small raised circle ° DEGREES An angle of 180° is called a straight angle. When two rays go in opposite directions and form a straight line, then the rays form a straight angle STRAIGHT ANGLE Classifying Angles Acute angles – measure less than 90° Right angles – measure exactly 90° Obtuse angles measure more than 90° but less than 180° Straight angles measure exactly 180° An angle of 90° is called a right angle. The rays of a right angle form one corner of a square. So, to show that an angle is a right angle, we draw a small square at the vertex. RIGHT ANGLE Classifying Angles Acute angles – measure less than 90° Right angles – measure exactly 90° Obtuse angles measure more than 90° but less than 180° Straight angles measure exactly 180° Acute angles measure less than 90° ACUTE ANGLE Classifying Angles Acute angles – measure less than 90° Right angles – measure exactly 90° Obtuse angles measure more than 90° but less than 180° Straight angles measure exactly 180° An Obtuse angle measures more than 90° but less than 180° OBTUSE ANGLE Classifying Angles Acute angles – measure less than 90° Right angles – measure exactly 90° Obtuse angles measure more than 90° but less than 180° Straight angles measure exactly 180° Two lines are called perpendicular lines if they intersect to form a right angle. PERPENDICULAR LINES Two angles are called complementary angles if the sum of their measures is 90°. If two angles are complementary , each angle is the complement of the other. COMPLEMENTARY ANGLES Two angles are called supplementary angles if the sum of their measures is 180° SUPPLEMENTARY ANGLES Two angles are called congruent angels if they measure the same number of degrees. If they are congruent, this is written as: Angle A is congruent to angle B CONGRUENT ANGLES Two nonadjacent (do NOT share a common side) angles formed by intersecting lines are called vertical angles. VERTICAL ANGLES Vertical Angles Are Congruent If two angles are vertical angles, they are congruent; that is, they measure the same number of degrees. When two parallel lines are crossed by a line (transversal line), four pairs of corresponding angles are formed. CORRESPONDING ANGLES When a transversal crosses two parallel lines, angles 3, 4, 5, and 6 are called interior angles. ALTERNATE INTERIOR ANGLES If two figures are identical in both shape and size then they are congruent CONGRUENT FIGURES/TRIANGLES Two useful concepts in geometry are congruence and similarity. • If two figures are identical in both shape and size then they are congruent. • If two figures have the same shape but different sizes then they are similar. If two figures have the same shape but different sizes then they are similar SIMILAR FIGURES/TRIANGLES Two useful concepts in geometry are congruence and similarity. • If two figures are identical in both shape and size then they are congruent. • If two figures have the same shape but different sizes then they are similar.