Postulates and Theorems from Chapter 1 Postulate 1: The Ruler Postulate 1. The points on a line can be paired with the real numbers in such a way that any two points can have coordinates 0 and 1. 2. Once a coordinate system has been chosen in this way, the distance between any two points equals the absolute value of the difference of their coordinates. Postulate 2: Segment Addition Postulate If B is between A and C, then: AB + BC = AC Postulate 3: Protractor Postulate 1. On line AB in a given plane, choose any point O between points A and B. Consider ray OA and ray OB and all the rays that can be drawn from O on one side of line AB. These rays can be paired with the real numbers from 0 to 180 in such a way that: a. Ray OA is paired with 0, and ray OB with 180. b. If ray OP is paired with x, and ray OQ with y, then the measure of angle POQ = x y. Postulate 4: Angle Addition Postulate If point B lies in the interior of angle AOC, then the measure of angle AOB + the measure of angle BOC = the measure of angle AOC. m AOB m BOC m AOC If angle AOC is a straight angle and B is any point not on line AC, then the measure of angle AOB + the measure of angle BOC = 180. m AOB m BOC 180 Postulate 5 A line contains at least two points; a plane contains at least three point not all in one line; space contains at least four points not all in one plane. Postulate 6 Through any two points there is exactly one line. Postulate 7 Through any three points there is at least one plane, and through any three noncollinear points there is exactly one plane. Postulate 8 If two points are in a plane, then the line that contains the points is in that plane. Postulate 9 If two planes intersect, then their intersection is a line. Theorem 1-1: If two lines intersect, then they intersect in exactly one point. Theorem 1-2: Through a line and a point not in the line there is exactly one plane. Theorem 1-3: If two lines intersect, then exactly one plane contains the lines.
Theorems from Chapter 2; Postulates and Theorems from Chapter 3 Theorem 2-1 / Midpoint Theorem: If M is the midpoint of segment AB, then AM = ½ AB and MB = ½ AB. Theorem 2-2 / Angle Bisector Theorem: If ray BX is the bisector of angle ABC, then the measure of angle ABX is one half the measure of angle ABC and the measure of angle XBC is one half the measure of angle ABC. 1 m ABX m XBC m ABC 2 Theorem 2-3: Vertical angles are congruent. Theorem 2-4: If two lines are perpendicular, then they form congruent adjacent angles. Theorem 2-5: If two lines form congruent adjacent angles, then the lines are perpendicular. Theorem 2-6: If the exterior sides of two adjacent acute angles are perpendicular, then the angles are complementary. Theorem 2-7: If two angles are supplements of congruent angles (or of the same angle), then the two angles are congruent. Theorem 2-8: If two angles are complements of congruent angles (or of the same angle), then the two angles are congruent. Theorem 3-1: If two parallel planes are cut by a third plane, then the lines of intersection are parallel. Postulate 10: If two parallel lines are cut by a transversal, then corresponding angles are congruent. Theorem 3-2: If two parallel lines are cut by a transversal, then alternate interior angles are congruent. Theorem 3-3: If two parallel lines are cut by a transversal, then same-side interior angles are supplementary. Theorem 3-4: If a transversal is perpendicular to one of two parallel lines, then it is perpendicular to the other one also. Postulate 11: If two lines are cut by a transversal and corresponding angles are congruent, then the lines are parallel Theorem 3-5: If two lines are cut by a transversal and alternate interior angles are congruent, then the lines are parallel. Theorem 3-6: If two lines are cut by a transversal and same-side interior angles are supplementary, then the lines are parallel. Theorem 3-7: In a plane two lines perpendicular to the same line are parallel Theorem 3-10: Two lines parallel to a third line are parallel to each other.
Theorems & Corollaries from Chapter 3; Postulates, Theorems & Corollaries from Chap. 4 Corollary to theorem 4-2: An equiangular triangle is also equilateral. Theorem 3-8: Through a point outside a line, there is exactly one line parallel to the given line. Theorem 3-9: Through a point outside a line, there is exactly one line perpendicular to the given line. Theorem 3-11: The sum of the measures of the angles of a triangle is 180. Corollary 1 to theorem 3-11: If two angles of one triangle are congruent to two angles of another triangle, then the third angles are congruent. Corollary 2 to theorem 3-11: Each angle of an equiangular triangle has measure 60. Corollary 3 to theorem 3-11: In a triangle, there can be at most one right angle or obtuse angle. Corollary 4 to theorem 3-11: The acute angles of a right triangle are complementary. Theorem 3-12: The measure of an exterior angle of a triangle equals the sum of the measures of the two remote interior angles. Theorem 3-13: The sum of the measures of the angles of a convex polygon with n sides is (n-2) 180. Theorem 3-14: The sum of the measures of the exterior angles of any convex polygon, one angle at each vertex, is 360. Postulate 12 (SSS Postulate): If three sides of one triangle are congruent to three sides of another triangle, then the triangles are congruent. Postulate 13 (SAS Postulate): If two sides and the included angle of one triangle are congruent to two sides and the included angle of another triangle, then the triangles are congruent. Postulate 14 (ASA Postulate): If two angles and the included side of one triangle are congruent to two angles and the included side of another triangle, then the triangles are congruent. Theorem 4-1 / Isosceles Triangle Theorem: If two sides of a triangle are congruent, then the angles opposite those sides are congruent. Corollary 1 to theorem 4-1: An equilateral triangle is also equiangular Corollary 2 to theorem 4-1: An equilateral triangle has 3 60 angles. Corollary 3 to theorem 4-1: The bisector of the vertex angle of an isosceles triangle is perpendicular to the base at its midpoint Theorem 4-2: If two angles of a triangle are congruent, then the sides opposite those angles are congruent.
Theorems from Chapter 4, continued; Theorems from Chapter 5 Theorem 4-3 / AAS Theorem: If two angles and a non-included side of one triangle are congruent to the corresponding parts of another triangle, then the triangles are congruent. Theorem 4-4 / HL Theorem: If the hypotenuse and a leg of one right triangle are congruent to the corresponding parts of another right triangle, then the triangles are congruent. Theorem 4-5: If a point lies on the perpendicular bisector of a segment, then the point is equidistant from the endpoints of the segment. Theorem 4-6: If a point is equidistant from the endpoints of a segment, then the point lies on the perpendicular bisector of the segment. Theorem 4-7: If a point lies on the bisector of an angle, then the point is equidistant from the sides of the angle. Theorem 4-8: If a point is equidistant from the sides of an angle, then the point lies on the bisector of the angle. Theorem 5-1: Opposite sides of a parallelogram are congruent. Theorem 5-2: Opposite angles of a parallelogram are congruent. Theorem 5-3: Diagonals of a parallelogram bisect each other. Theorem 5-4: If both pairs of opposite sides of a quadrilateral are congruent, then the quadrilateral is a parallelogram. Theorem 5-5: If one pair of opposite sides of a quadrilateral are both congruent and parallel, then the quadrilateral is a parallelogram. Theorem 5-6: If both pairs of opposite angles of a quadrilateral are congruent, then the quadrilateral is a parallelogram. Theorem 5-7: If the diagonals of a quadrilateral bisect each other, then the quadrilateral is a parallelogram. Theorem 5-8: If two lines are parallel, then all points on one line are equidistant from the other line. Theorem 5-9: If three parallel lines cut off congruent segments on one transversal, then they cut off congruent segments on every transversal. Theorem 5-10: A line that contains the midpoint of one side of a triangle and is parallel to another side passes through the midpoint of the third side. Theorem 5-11: The segment that joins the midpoints of two sides of a triangle (1) is parallel to the third side and (2) is half as long as the third side.
Theorems from Chapter 5, continued; Theorems and Corollaries from Chapter 6 Theorem 5-12: The diagonals of a rectangle are congruent. Theorem 5-13: The diagonals of a rhombus are perpendicular. Theorem 5-14: Each diagonal of a rhombus bisects two angles of the rhombus. Theorem 5-15: The midpoint of the hypotenuse of a right triangle is equidistant from the three vertices. Theorem 5-16: If an angle of a parallelogram is a right angle, then the parallelogram is a rectangle. Theorem 5-17: If two consecutive sides of a parallelogram are congruent, then the parallelogram is a rhombus. Theorem 5-18: Base angles of an isosceles trapezoid are congruent. Theorem 5-19: The median of a trapezoid (1) is parallel to the bases and (2) has a length equal to the average of the base lengths Theorem 6-1: The Exterior Angle Inequality Theorem: The measure of an exterior angle of a triangle is greater than the measure of either remote interior angle. Theorem 6-2: If one side of a triangle is longer than a second side, then the angle opposite the first side is larger than the angle opposite the second side. Theorem 6-3: If one angle of a triangle is larger than a second angle, then the side opposite the first angle is longer than the side opposite the second angle. Corollary 1 to theorem 6-3: The perpendicular segment from a point to a line is the shortest segment from the point to the line. Corollary 2 to theorem 6-3: The perpendicular segment from a point to a plane is the shortest segment from the point to the plane. Theorem 6-4: The sum of the lengths of any two sides of a triangle is greater than the length of the third side. Theorem 6-5: SAS Inequality Theorem: If two sides of one triangle are congruent to two sides of another triangle, but the included angle of the first triangle is larger than the included angle of the second triangle, then the third side of the first triangle is longer than the third side of the second triangle. Theorem 6-6: SSS Inequality Theorem: If two sides of one triangle are congruent to two sides of another triangle, but the third side of the first triangle is longer than the third side of the second triangle, then the included angle of the first triangle is larger than the included angle of the second.
Postulates, Theorems & Corollaries from Chapter 7; Theorems & Corollaries from Chapt. 8 Postulate 15: AA Similarity Postulate: If two angles of one triangle are congruent to two angles of another triangle, then the triangles are similar. Theorem 7-1: SAS Similarity Theorem: If an angle of one triangle is congruent to an angle of another triangle and the sides including those angles are in proportion, then the triangles are similar. Theorem 7-2: SSS Similarity Theorem: If the sides of two triangles are in proportion, then the triangles are similar. Theorem 7-3: Triangle Proportionality Theorem: If a line parallel to one side of a triangle intersects the other two sides, then it divides those sides proportionally. Corollary to Theorem 7-3: If three parallel lines intersect two transversals, then they divide the transversals proportionally. Theorem 7-4: Triangle Angle-Bisector Theorem: If a ray bisects an angle of a triangle, then it divides the opposite side into segments proportional to the other two sides. Theorem 8-1: If the altitude is drawn to the hypotenuse of a right triangle, then the two triangles formed are similar to the original triangle and to each other. Corollary 1 to theorem 8-1: When the altitude is drawn to the hypotenuse of a right triangle, the length of the altitude is the geometric mean between the segments of the hypotenuse. Corollary 2 to theorem 8-1: When the altitude is drawn to the hypotenuse of a right triangle, each leg is the geometric mean between the hypotenuse and the segment of the hypotenuse that is adjacent to the leg. Theorem 8-2: The Pythagorean Theorem: In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the legs. Theorem 8-3: If the square of one side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right triangle. Theorem 8-4: If the square of one side of a triangle is less than the sum of the squares of the other two sides, then the triangle is acute. Theorem 8-5: If the square of one side of a triangle is greater than the sum of the squares of the other two sides, then the triangle is obtuse. Theorem 8-6: 45-45 -90 Theorem: In a 45-45 -90 triangle, the hypotenuse is 2 times as long as a leg. Theorem 8-7: 30-60 -90 Theorem: In a 30-60 -90 triangle, the hypotenuse is twice as long as the shorter leg, and the longer leg is 3 times as long as the shorter leg.
: A Post., Theor s & Cor s from Ch. 9 Theorem 9-1: If a line is tangent to a circle, then the line is perpendicular to the radius drawn to the point of tangency. Corollary to theorem 9-1: Tangents to a circle from a point are congruent. Theorem 9-2: If a line in the plane of a circle is perpendicular to a radius at its outer endpoint, then the line is tangent to the circle. Postulate 16: Arc Addition Postulate: The measure of the arc formed by two adjacent arcs is the sum of the measures of these two arcs. Theorem 9-3: In the same circle or in congruent circles, two minor arcs are congruent if and only if their central angles are congruent. Theorem 9-4: In the same circle or in congruent circles: (1) Congruent arcs have congruent chords. (2) Congruent chords have congruent arcs. Theorem 9-5: A diameter that is perpendicular to a chord bisects the chord and its arc. Theorem 9-6: In the same circle or in congruent circles: (1) Chords equally distant from the center (or centers) are congruent. (2) Congruent chords are equally distant from the center (or centers). Theorem 9-7: The measure of an inscribed angle is equal to half the measure of its intercepted arc. Corollary 1 to theorem 9-7: If two inscribed angles intercept the same arc, then the angles are congruent. Corollary 2 to theorem 9-7: An angle inscribed in a semicircle is a right angle. Corollary 3 to theorem 9-7: If a quadrilateral is inscribed in a circle, then its opposite angles are suppl. Theorem 9-8: The measure of an angle formed by a chord and a tangent is equal to half the measure of the intercepted arc. Theorem 9-9: The measure of an angle formed by two chords that intersect inside a circle is equal to half the sum of the measures of the intercepted arcs. Theorem 9-10: The measure of an angle formed by two secants, two tangents, or a secant and a tangent drawn from a point outside a circle is equal to half the difference of the measures of the intercepted arcs. Theorem 9-11: When two chords intersect inside a circle, the product of the segments of one chord equals the product of the segments of the other chord. Theorem 9-12: When two secant segments are drawn to a circle from an external point, the product of one secant segment and its external segment equals the product of the other secant segment and its ext. seg. Theorem 9-13: When a secant segment and a tangent segment are drawn to a circle from an external point, the product of the secant segment and its external segment is equal to the square of the tangent seg.