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Example • Describe a pattern in the sequence of numbers. Predict the next number. • 1, 4, 16, 64, …. Each number is 4 times the previous number. • -5, -2, 4, 13, … 256 25 +3 +6 +9 +12
Definition • Conjecture • An unproven statement that is based on observations. • Inductive reasoning • Looking for patterns and making conjectures
Complete the conjecture. • Conjecture: The sum of the first n odd positive integer is ______ 1 1 + 3 1 + 3 + 5 1 + 3 + 5 + 7 n2 = 1 = 12 = 4 = 22 = 9 = 32 = 16 = 42
Finding and Describing Patterns • Describe a pattern in the sequence of numbers. Predict the next number. • 4, 16, 36, 64, … • 4.4, 40.4, 400.4, 4000.4, …
Definitions • Point has no dimension. It is usually represented by a small dot. • Line extends in one dimension. It is usually represented by a straight line with two arrowheads. • Plane extends in two dimensions. It is usually represented by a shape that looks like a tabletop or wall.
more definitions… • Collinear points are points that lie on the same line. • Coplanar points are points that lie on the same plane. • Ray consists of the initial point. • Intersect means to have one or more points in common.
Decide whether the statement is true or false * True • Point A lines on line l. • Point C lies on line m. • A,B, and C are collinear. • D,E, and B are coplanar. • A,B, and C are coplanar. m . l . False D A False True . E True . C . B .
Sketch the figure described • Three points that are coplanar but not collinear. • Three lines that intersect in a point and all lie in the same plane. • Two planes that do not intersect. • Three planes that intersect in a line. • Two lines that lie in a plane but do not intersect.
Definitions • Postulates: rules that are accepted without proof. • Theorems: rules that are proved. • Axioms: rules that are accepted without proof.
Segment Addition Postulate * If B is between A and C, then AB + BC = AC. If AB + BC = AC, then B is between A and C. . . . C A B
Examples • In the diagram of the collinear points, PT=20, QS=6, and PQ = QR = RS. Find each length. • QR • RS • RT • RP • SP T . S . . Q R P
1. AB = 6x + 16 BC = 2x – 5 AC = 46 2. AB = ½ k + 4 BC = 3k – 4 AC = 6k – 18 Suppose B is between A and C. Use the segment addition postulate to solve for the variable.
Congruent? AB = AD AB is equal to AD Segment AB is congruent to segment AD
The distance formula The distance formula is formula for computing the distance between two points in a coordinate plane. Pythagorean Theorem c2 = a2 + b2 c a b
Examples • Find the distance between each pair of points • A(-4, 7) B(6,2) • C(-3, 6) D(0,2) • E(1,4) F(4, -4)
Review • Determine if the statement is true or false. • E lies on BD. • A, B, and D are collinear. • B lies in plane ADC. • The intersection of DE and AC is B. . D . . B . C A . E
Definition of an Angle • Angle consists of two different rays that have the same initial point . C Sides Vertex . . A B
Angle addition postulate • If P is in the interior of <RST, then m<RSP + m<PST = m<RST . R P . m<RSP . S m<PST . T
Example • Use the Angle Addition Postulate to find the measure of the unknown angle. m<ABC= . D C . . A 45° 60° . B
Different types of angles * Supplementary angles Straight angle Acute angle Obtuse angle Right angle Complementary angles
Review • Plot the given points and classify the given angles as acute, right, obtuse, or straight. A(-2,4), B(-5,1), C(0,0), and D(3,0) • <ACB • <BCD • <ACD
Draw a sketch that uses all of the following information. • D is in the interior of <BAE. • E is in the interior of <DAF. • F is in the interior of <EAC. • m<BAC = 130° • m<EAC = 100° • m<BAD = m<EAF = m<FAC • Now find m<FAC • Find m<BAD • Find m<BAE
Warmup • Fill in the blanks. • The end point of RQ is _______. • Line segments with equal measures are ___________. • A rule of geometry that is accepted without proof is a _______________. • A pair of opposite rays form a ________. Q congruent postulate or axiom line
Midpoint Formula x2 x1 Example: Find the midpoint of (-2,3) and (5,-2) y2 y1
More examples… • Find the coordinates of the midpoint. 1. A(-7, 2), B(3,0) 2. K(7,3), L(2,1)
Challenge question • The midpoint of RP is M(2,4). One endpoint is R(-1,7). Find the coordinates of the other endpoint.
Segment Bisector and Midpoint • Draw a segment AB. • Place the compass point at A. Use a compass setting greater than half the length of AB. Draw an arc. • Keep the same compass setting. Place the compass point at B. Draw an arc. It should intersect the other arc in two places. • Use a straightedge to draw a segment through the points of intersection. This segment bisects AB at M, the midpoint of AB.
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