# Angles § 3.1 Angles § 3.2 Angle Measure

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Angles § 3.1 Angles § 3.2 Angle Measure
§ 3.3 The Angle Addition Postulate § 3.4 Adjacent Angles and Linear Pairs of Angles § 3.5 Complementary and Supplementary Angles § 3.6 Congruent Angles § 3.7 Perpendicular Lines

Vocabulary What You'll Learn
Angles What You'll Learn You will learn to name and identify parts of an angle. Vocabulary 1) Opposite Rays 2) Straight Angle 3) Angle 4) Vertex 5) Sides 6) Interior 7) Exterior

XY and XZ are ____________. opposite rays
Angles Opposite rays ___________ are two rays that are part of a the same line and have only their endpoints in common. X Y Z XY and XZ are ____________. opposite rays The figure formed by opposite rays is also referred to as a ____________. straight angle

There is another case where two rays can have a common endpoint.
Angles There is another case where two rays can have a common endpoint. This figure is called an _____. angle Some parts of angles have special names. S The common endpoint is called the ______, vertex and the two rays that make up the sides of the angle are called the sides of the angle. side R T side vertex

There are several ways to name this angle.
Angles There are several ways to name this angle. 1) Use the vertex and a point from each side. SRT or TRS S The vertex letter is always in the middle. 2) Use the vertex only. side R If there is only one angle at a vertex, then the angle can be named with that vertex. 1 R T side vertex 3) Use a number. 1

Angles Definition of Angle An angle is a figure formed by two noncollinear rays that have a common endpoint. E D F 2 Symbols: DEF FED E 2

1) Name the angle in four ways.
Angles 1) Name the angle in four ways. B A 1 C ABC CBA B 1 2) Identify the vertex and sides of this angle. vertex: Point B sides: BA and BC

1) Name all angles having W as their vertex.
2 1 W 2 XWZ Y 2) What are other names for ? 1 Z XWY or YWX 3) Is there an angle that can be named ? W No!

An angle separates a plane into three parts:
1) the ______ interior exterior 2) the ______ exterior W Y Z A interior 3) the _________ angle itself In the figure shown, point B and all other points in the blue region are in the interior of the angle. B Point A and all other points in the green region are in the exterior of the angle. Points Y, W, and Z are on the angle.

Angles Is point B in the interior of the angle, exterior of the angle, or on the angle? P G Exterior B Is point G in the interior of the angle, exterior of the angle, or on the angle? On the angle Is point P in the interior of the angle, exterior of the angle, or on the angle? Interior

Vocabulary What You'll Learn
§3.2 Angle Measure What You'll Learn You will learn to measure, draw, and classify angles. Vocabulary 1) Degrees 2) Protractor 3) Right Angle 4) Acute Angle 5) Obtuse Angle

In geometry, angles are measured in units called _______. degrees
§3.2 Angle Measure In geometry, angles are measured in units called _______. degrees The symbol for degree is °. Q P R 75° In the figure to the right, the angle is 75 degrees. In notation, there is no degree symbol with 75 because the measure of an angle is a real number with no unit of measure. m PQR = 75

Angles Measure Postulate
§3.2 Angle Measure Postulate 3-1 Angles Measure Postulate For every angle, there is a unique positive number between __ and ____ called the degree measure of the angle. 180 B A C m ABC = n and 0 < n < 180

Use a protractor to measure SRQ.
§3.2 Angle Measure You can use a _________ to measure angles and sketch angles of given measure. protractor Use a protractor to measure SRQ. 1) Place the center point of the protractor on vertex R Align the straightedge with side RS. Q R S 2) Use the scale that begins with at RS Read where the other side of the angle, RQ, crosses this scale.

Find the measurement of: m SRH 70
§3.2 Angle Measure Find the measurement of: m SRH 70 m SRQ = 180 m QRG = 180 – 150 = 30 m SRJ = 45 m GRJ = 150 – 45 = 105 m SRG = 150 H J G S Q R

Use a protractor to draw an angle having a measure of 135.
§3.2 Angle Measure Use a protractor to draw an angle having a measure of 135. 1) Draw AB 3) Locate and draw point C at the mark labeled Draw AC. 2) Place the center point of the protractor on A. Align the mark labeled 0 with the ray. C A B

obtuse angle 90 < m A < 180 right angle m A = 90
§3.2 Angle Measure Once the measure of an angle is known, the angle can be classified as one of three types of angles. These types are defined in relation to a right angle. Types of Angles A A A obtuse angle 90 < m A < 180 right angle m A = 90 acute angle 0 < m A < 90

Classify each angle as acute, obtuse, or right.
§3.2 Angle Measure Classify each angle as acute, obtuse, or right. 110° 90° 40° Obtuse Right Acute 75° 50° 130° Acute Obtuse Acute

The measure of B is 138. Solve for x.
§3.2 Angle Measure 5x - 7 B The measure of B is 138. Solve for x. 9y + 4 H The measure of H is 67. Solve for y. Given: (What do you know?) Given: (What do you know?) B = 5x – 7 and B = 138 H = 9y and H = 67 5x – 7 = 138 9y + 4 = 67 Check! Check! 5x = 145 9y = 63 5(29) -7 = ? 9(7) + 4 = ? x = 29 y = 7 = ? = ? 138 = 138 67 = 67

? ? ? Is m a larger than m b ? 60° 60°

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What You'll Learn You will learn to find the measure of an angle and the bisector of an angle. Vocabulary NOTHING NEW!

1) Draw an acute, an obtuse, or a right angle Label the angle RST. R T S 45° 2) Draw and label a point X in the interior of the angle. Then draw SX. X 75° 30° 3) For each angle, find mRSX, mXST, and RST.

1) How does the sum of mRSX and mXST compare to mRST ? Their sum is equal to the measure of RST . mXST = 30 + mRSX = 45 = mRST = 75 R T S 2) Make a conjecture about the relationship between the two smaller angles and the larger angle. 45° X The sum of the measures of the two smaller angles is equal to the measure of the larger angle. The Angle Addition Postulate (Video) 75° 30°

For any angle PQR, if A is in the interior of PQR, then mPQA + mAQR = mPQR. 2 1 A R P Q m1 + m2 = mPQR. There are two equations that can be derived using Postulate 3 – 3. m1 = mPQR – m2 These equations are true no matter where A is located in the interior of PQR. m2 = mPQR – m1

Find m2 if mXYZ = 86 and m1 = 22. 2 1 Y Z X W m2 + m1 = mXYZ Postulate 3 – 3. m2 = mXYZ – m1 m2 = 86 – 22 m2 = 64

Find mABC and mCBD if mABD = 120. mABC + mCBD = mABD Postulate 3 – 3. 2x + (5x – 6) = 120 Substitution 7x – 6 = 120 Combine like terms 7x = 126 Add 6 to both sides x = 18 Divide each side by 7 = 120 2x° (5x – 6)° B D C A mABC = 2x mCBD = 5x – 6 mABC = 2(18) mCBD = 5(18) – 6 mABC = 36 mCBD = 90 – 6 mCBD = 84

Just as every segment has a midpoint that bisects the segment, every angle has a ___ that bisects the angle. ray This ray is called an ____________ . angle bisector

Definition of an Angle Bisector The bisector of an angle is the ray with its endpoint at the vertex of the angle, extending into the interior of the angle. The bisector separates the angle into two angles of equal measure. 2 1 A R P Q is the bisector of PQR. m1 = m2

If bisects CAN and mCAN = 130, find 1 and 2. Since bisects CAN, 1 = 2. 1 2 A C N T 1 + 2 = CAN Postulate 3 - 3 1 + 2 = 130 Replace CAN with 130 1 + 1 = 130 Replace 2 with 1 2(1) = 130 Combine like terms (1) = 65 Divide each side by 2 Since 1 = 2, 2 = 65

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Adjacent Angles and Linear Pairs of Angles
What You'll Learn You will learn to identify and use adjacent angles and linear pairs of angles. A C B When you “split” an angle, you create two angles. D The two angles are called _____________ adjacent angles 2 1 adjacent = next to, joining. 1 and 2 are examples of adjacent angles. They share a common ray. Name the ray that 1 and 2 have in common. ____

Adjacent Angles and Linear Pairs of Angles
Definition of Adjacent Angles Adjacent angles are angles that: A) share a common side B) have the same vertex, and C) have no interior points in common M J N R 1 2 1 and 2 are adjacent with the same vertex R and common side

Adjacent Angles and Linear Pairs of Angles
Determine whether 1 and 2 are adjacent angles. No. They have a common vertex B, but _____________ 1 2 B no common side Yes. They have the same vertex G and a common side with no interior points in common. 1 2 G N 1 2 J L No. They do not have a common vertex or ____________ a common side The side of 1 is ____ The side of 2 is ____

Adjacent Angles and Linear Pairs of Angles
Determine whether 1 and 2 are adjacent angles. No. 1 2 Yes. 1 2 X D Z In this example, the noncommon sides of the adjacent angles form a ___________. straight line These angles are called a _________ linear pair

Adjacent Angles and Linear Pairs of Angles
Definition of Linear Pairs Two angles form a linear pair if and only if (iff): A) they are adjacent and B) their noncommon sides are opposite rays C A D B 1 2 1 and 2 are a linear pair. Note:

Adjacent Angles and Linear Pairs of Angles
In the figure, and are opposite rays. 1 2 M 4 3 E H T A C 1) Name the angle that forms a linear pair with 1. ACE ACE and 1 have a common side , the same vertex C, and opposite rays and 2) Do 3 and TCM form a linear pair? Justify your answer. No. Their noncommon sides are not opposite rays.

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§3.5 Complementary and Supplementary Angles
What You'll Learn You will learn to identify and use Complementary and Supplementary angles

§3.5 Complementary and Supplementary Angles
Definition of Complementary Angles Two angles are complementary if and only if (iff) the sum of their degree measure is 90. 60° D E F 30° A B C mABC + mDEF = = 90

§3.5 Complementary and Supplementary Angles
If two angles are complementary, each angle is a complement of the other. ABC is the complement of DEF and DEF is the complement of ABC. 60° D E F 30° A B C Complementary angles DO NOT need to have a common side or even the same vertex.

§3.5 Complementary and Supplementary Angles
Some examples of complementary angles are shown below. 75° I mH + mI = 90 15° H 50° H 40° Q P S mPHQ + mQHS = 90 30° 60° T U V W Z mTZU + mVZW = 90

§3.5 Complementary and Supplementary Angles
If the sum of the measure of two angles is 180, they form a special pair of angles called supplementary angles. Definition of Supplementary Angles Two angles are supplementary if and only if (iff) the sum of their degree measure is 180. 130° D E F 50° A B C mABC + mDEF = = 180

§3.5 Complementary and Supplementary Angles
Some examples of supplementary angles are shown below. 105° H 75° I mH + mI = 180 50° H 130° Q P S mPHQ + mQHS = 180 60° 120° T U V W Z mTZU + mUZV = 180 and mTZU + mVZW = 180

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What You'll Learn You will learn to identify and use congruent and
§3.6 Congruent Angles What You'll Learn You will learn to identify and use congruent and vertical angles. Recall that congruent segments have the same ________. measure _______________ also have the same measure. Congruent angles

Two angles are congruent iff, they have the same ______________.
§3.6 Congruent Angles Definition of Congruent Angles Two angles are congruent iff, they have the same ______________. degree measure B  V iff 50° V mB = mV 50° B

To show that 1 is congruent to 2, we use ____. arcs
§3.6 Congruent Angles To show that 1 is congruent to 2, we use ____. arcs 1 2 To show that there is a second set of congruent angles, X and Z, we use double arcs. This “arc” notation states that: Z X X  Z mX = mZ

When two lines intersect, ____ angles are formed. four
§3.6 Congruent Angles When two lines intersect, ____ angles are formed. four There are two pair of nonadjacent angles. These pairs are called _____________. vertical angles 1 4 2 3

Two angles are vertical iff they are two nonadjacent
§3.6 Congruent Angles Definition of Vertical Angles Two angles are vertical iff they are two nonadjacent angles formed by a pair of intersecting lines. Vertical angles: 1 and 3 1 4 2 2 and 4 3

Hands-On 1) On a sheet of paper, construct two intersecting lines
§3.6 Congruent Angles 1) On a sheet of paper, construct two intersecting lines that are not perpendicular. 2) With a protractor, measure each angle formed. 3) Make a conjecture about vertical angles. 1 2 3 4 Consider: A. 1 is supplementary to 4. m1 + m4 = 180 Hands-On B. 3 is supplementary to 4. m3 + m4 = 180 Therefore, it can be shown that 1  3 Likewise, it can be shown that 2  4

1) If m1 = 4x + 3 and the m3 = 2x + 11, then find the m3
§3.6 Congruent Angles 1 2 3 4 1) If m1 = 4x + 3 and the m3 = 2x + 11, then find the m3 x = 4; 3 = 19° 2) If m2 = x + 9 and the m3 = 2x + 3, then find the m4 x = 56; 4 = 65° 3) If m2 = 6x - 1 and the m4 = 4x + 17, then find the m3 x = 9; 3 = 127° 4) If m1 = 9x - 7 and the m3 = 6x + 23, then find the m4 x = 10; 4 = 97°

Vertical angles are congruent.
§3.6 Congruent Angles Theorem 3-1 Vertical Angle Theorem Vertical angles are congruent. n m 2 1  3 3 1 2  4 4

Find the value of x in the figure:
§3.6 Congruent Angles Find the value of x in the figure: The angles are vertical angles. 130° So, the value of x is 130°.

Find the value of x in the figure:
§3.6 Congruent Angles Find the value of x in the figure: The angles are vertical angles. (x – 10) = 125. (x – 10)° x – 10 = 125. 125° x = 135.

Suppose two angles are congruent.
§3.6 Congruent Angles Suppose two angles are congruent. What do you think is true about their complements? 1  2 1 + x = 90 2 + y = 90 x is the complement of 1 y is the complement of 2 x = 90 - 1 y = 90 - 2 Because 1  2, a “substitution” is made. x = 90 - 1 y = 90 - 1 x = y x  y If two angles are congruent, their complements are congruent.

If two angles are congruent, then their complements are _________.
§3.6 Congruent Angles Theorem 3-2 If two angles are congruent, then their complements are _________. congruent The measure of angles complementary to A and B is 30. A B 60° A  B Theorem 3-3 If two angles are congruent, then their supplements are _________. congruent The measure of angles supplementary to 1 and 4 is 110. 4 3 2 1 70° 110° 110° 70° 4  1

If two angles are complementary to the same angle,
§3.6 Congruent Angles Theorem 3-4 If two angles are complementary to the same angle, then they are _________. congruent 3 is complementary to 4 5 is complementary to 4 4 3 5  3 5 Theorem 3-5 If two angles are supplementary to the same angle, then they are _________. congruent 3 1 2 1 is supplementary to 2 3 is supplementary to 2 1  3

Find the measure of an angle that is supplementary to B.
§3.6 Congruent Angles Suppose A  B and mA = 52. Find the measure of an angle that is supplementary to B. A 52° B 52° 1 B + 1 = 180 1 = 180 – B 1 = 180 – 52 1 = 128°

If 1 is complementary to 3, 2 is complementary to 3, and m3 = 25,
§3.6 Congruent Angles If 1 is complementary to 3, 2 is complementary to 3, and m3 = 25, What are m1 and m2 ? m1 + m3 = Definition of complementary angles. m1 = 90 - m Subtract m3 from both sides. m1 = Substitute 25 in for m3. m1 = Simplify the right side. You solve for m2 m2 + m3 = Definition of complementary angles. m2 = 90 - m Subtract m3 from both sides. m2 = Substitute 25 in for m3. m2 = Simplify the right side.

1) If m1 = 2x + 3 and the m3 = 3x - 14, then find the m3
§3.6 Congruent Angles A B C D E G H 1 2 3 4 1) If m1 = 2x + 3 and the m3 = 3x - 14, then find the m3 x = 17; 3 = 37° 2) If mABD = 4x + 5 and the mDBC = 2x + 1, then find the mEBC x = 29; EBC = 121° 3) If m1 = 4x and the m3 = 2x + 19, then find the m4 x = 16; 4 = 39° 4) If mEBG = 7x and the mEBH = 2x + 7, then find the m1 x = 18; 1 = 43°

Suppose you draw two angles that are congruent and supplementary.
What is true about the angles?

All right angles are _________. congruent
§3.6 Congruent Angles Theorem 3-6 If two angles are congruent and supplementary then each is a __________. right angle 1 is supplementary to 2 1 2 1 and 2 = 90 Theorem 3-7 All right angles are _________. congruent C B A A  B  C

If 1 is supplementary to 4, 3 is supplementary to 4, and
§3.6 Congruent Angles If 1 is supplementary to 4, 3 is supplementary to 4, and m 1 = 64, what are m 3 and m 4? A D C B E 1 2 3 4 1  3 They are vertical angles. m 1 = m3 m 3 = 64 3 is supplementary to 4 Given m3 + m4 = 180 Definition of supplementary. 64 + m4 = 180 m4 = 180 – 64 m4 = 116

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§3.7 Perpendicular Lines What You'll Learn You will learn to identify, use properties of, and construct perpendicular lines and segments.

Lines that intersect at an angle of 90 degrees are _________________.
§3.7 Perpendicular Lines Lines that intersect at an angle of 90 degrees are _________________. perpendicular lines In the figure below, lines are perpendicular. A D C B 1 2 3 4

Perpendicular lines are lines that intersect to form a right angle.
Definition of Perpendicular Lines Perpendicular lines are lines that intersect to form a right angle. m n

In the figure below, l  m. The following statements are true.
§3.7 Perpendicular Lines In the figure below, l  m. The following statements are true. m 2 1 3 4 l 1) 1 is a right angle. Definition of Perpendicular Lines 2) 1  3. Vertical angles are congruent 3) 1 and 4 form a linear pair. Definition of Linear Pair 4) 1 and 4 are supplementary. Linear pairs are supplementary 5) 4 is a right angle. m = 180, m4 = 90 6) 2 is a right angle. Vertical angles are congruent

If two lines are perpendicular, then they form four right angles.
§3.7 Perpendicular Lines Theorem 3-8 If two lines are perpendicular, then they form four right angles. 1 3 4 2 a b

1) PRN is an acute angle. False. 2) 4  8 True
§3.7 Perpendicular Lines 1) PRN is an acute angle. False. 2) 4  8 True

If a line m is in a plane and T is a point in m, then there
§3.7 Perpendicular Lines Theorem 3-9 If a line m is in a plane and T is a point in m, then there exists exactly ___ line in that plane that is perpendicular to m at T. one m T

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