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2.6 algebraic proofs ink.notebook
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September 13, 2017
2.6 algebraic proofs
Page 70Page 71 Page 72
Page 73Lesson Objectives Standards Lesson Notes
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2.6 Algebraic Proofs
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Lesson Objectives
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Lesson NotesStandards
After this lesson, you should be able to successfully apply algebraic properties to write proofs.
Lesson Objectives Standards
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Lesson Notes
G.CO.9 Prove theorems about lines and angles.
A list of algebraic steps to solve problems where each step is justified is called an algebraic proof, The table shows properties you have studied in algebra. Reflexive Property
of EqualitySymmetric Property
of Equality
Substitution Property of Equality
Transitive Property of Equality
Subtraction Property of Equality
Addition Property of Equality
Division Property of Equality
Multiplication Property of Equality
If a = b, then a + c = b + c
If a = b, then a - c = b - c
If a = b, then ac = bc
a = a If a = b, then b = a
If a = b and b = c, then a = c
If a = b, then a may be replaced by b in any equation
If a = b and c = 0, then ac
bc=
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Distributive Property:
a(b + c) = ab + bc
Example 1: Solve 2x + 3 = 9 − x. Write a reason for each step.
Equation Explanation Reason
2x + 3 = 9 x Rewrite the original equation
2x + 3 + ____ = 9 x + ____ Add _____ to each side
________ + 3 = ________ Combine like terms
__________ = __________ Subtract _____ from each side
x = _____ Divide each side by _____
Division Property
AdditionProperty
Given
Substitution
Subtraction Property
Equation Explanation Reason
4(6x + 2) = 64 Rewrite the original equation
__________________ = 64 Multiply
_________ = _________ Add _____ to each side
x = _____Divide each side by
_____Division Property
AdditionProperty
Given
Example 2: Solve 4(6x + 2) = 64. Write a reason for each step.
*Do not have to show the substitution step to show you simplified!!
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Property Segments AnglesReflexive AB = AB m<1 = m<1
Symmetric If AB = CD, then CD = AB.
If m<1 = m<2, then m<2 = m<1.
Transitive If AB = CD and CD = EF, then AB = EF.
If m<1 = m<2 and m<2 = m<3, then m<1 = m<3.
In geometry, a similar format is usedà two column proof or formal proofStatements and reasons organized in two columnsEach step is called ________________Properties that justify each step are called _____________
Geometric Proof Geometry deals with numbers as measures, so geometric proofs use properties of numbers. Here are some of the algebraic properties used in geometric proofs.
StatementReason
Example 3: Write a twocolumn proof to verify this conjecture.
Given: m⁄1 = m⁄2, m⁄2 = m⁄3
Prove: m⁄1 = m⁄3
Statements Reasons
1. _____________
2. _____________
3. _____________
1. m⁄1 = m⁄2
2. m⁄2 = m⁄3
3. m⁄1 = m⁄3
Given
TransitiveGiven
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State the property that justifies each statement.
1. If m∠1 = m∠2, then m∠2 = m∠1.
Symmetric PropertyTransitive Property Reflexive Property
2. If m∠1 = 90 and m∠2 = m∠1, then m∠2 = 90.Substitution Property Transitive PropertySymmetric Property
3. If AB = RS and RS = WY, then AB = WY.
Symmetric PropertyTransitive Property Reflexive Property
4. If AB = CD, then
Substitution Property Addition Property Multiplication Property
5. If m∠1 + m∠2 = 110 and m∠2 = m∠3, then m∠1 + m∠3 = 110.
Symmetric Property Substitution Property Transitive Property
6. RS = RS
Symmetric PropertyTransitive Property Reflexive Property
7. If AB = RS and TU = WY, then AB + TU = RS + WY.Substitution Property Addition Property Multiplication Property
8. If m∠1 = m∠2 and m∠2 = m∠3, then m∠1 = m∠3.
Symmetric PropertyTransitive Property Substitution Property
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Practice
More Practice – 2.6 State the property that justifies each statement.1. If 80 = m⁄A, then m⁄A = 80.
2. If RS = TU and TU = YP, then RS = YP.
3. If 7x = 28, then x = 4.
4. If VR + TY = EN + TY, then VR = EN.
5. If m⁄1 = 30 and m⁄1 = m⁄2, then m⁄2 = 30.
Given: 8x − 5 = 2x + 1 Prove: x = 1Complete the following proof.
6.
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Prove: x = 3
9. Given: 4x + 8 = x + 2 Prove: x = −2Answers:
1. Symmetric 3. Division 5. Substitution
7. J, D, E, G, H, A, C, F, I, B
9. Given, subtraction, 3x + 8 – 8 = 2 – 8, 3x = −6, division, x = −2
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+ BOOK WORK
p. 137(918, 43, 56 58)
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Check book work answers to the odd problems in the back of the book