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CHAPTER3.6Y
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à 3.6èMedian, Altitudues, å Isosceles Triangles
äèPlease answer ê followïg questions about medians,
altitudes, å isosceles triangles.
â
èèèèèèèTwo sides ç a triangle are equal if å onlyè
èèèèèèèif ê angles opposite êse sides are equal.
éS In this section we will restate ê defïition ç isosceles tri-
angles å develop some facts about ê angles ç êse triangles.èIn
addition we will look at ê defïitions ç median, altitude, å angle
bisecër ç a triangle.
Defïition 3.1.7èISOSCELES TRIANGLE:èAn isosceles triangle is a tri-
angle with two equal sides.èThe third side is called ê base.
Defïition 3.6.1èMEDIAN:èA median ç a triangle is ê lïe segment
joïïg a vertex ë ê midpoït ç ê opposite side.
Defïition 3.6.2èALTITUDE:èAn altitude ç a triangle is a lïe segment
from a vertex perpendicular ë ê opposite side.
Defïition 3.6.3èANGLE BISECTOR OF A TRIANGLE:èAn angle bisecër ç a
triangle is a lïe segment that extends from a vertex ë ê side oppo-
site ï such a way that it bisects ê angle at ê vertex.
Theorem 3.6.1èTwo sides ç a triangle are congruent if å only if ê
angles opposite êse sides are congruent.
Proç:èFor a prove please see Problems 1 å 2.
Theorem 3.6.2èA triangle is equilateral if å only if it is
equiangular.
Proç:èFor a proç please see Problems 3 å 4.
Theorem 3.6.3èIf an hypotenuse å leg ç one right triangle are con-
gruent ë ê correspondïg parts ç anoêr right triangle, ên ê
triangles are congruent.
1èèèèèèèèèèIf ▒┤ ╧ ┤╖, can you show that ╬A ╧ ╬C?
èèèèèèèèèèèèè(Show angles opposite equal sides are equal.)è
@fig3601.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ╬A ╧ ╬C
Proç: Statementèèèèèèèèèèèèè Reason
èèè 1. ▒┤ ╧ ┤╖èèèèèèèèèèèèè1. Given
èèè 2. Constuct angle bisecër ┤╗èèè 2. An angle can be bisected
èèè 3. ╬ABE ╧ ╬CBEèèèèèèèèèèè3. Defïition ç bisecër
èèè 4. ┤║ ╧ ┤║èèèèèèèèèèèèè4. Congruence is reflexive
èèè 5. ΦABE ╧ ΦCBEèèèèèèèèèèè5. Congruent by SAS
èèè 6. ╬A ╧ ╬Cèèèèèèèèèèèèè6. Correspondïg parts ç
èèèèèèèèèèèèèèèèèèèèèèèècongruent Φs
Ç A
2èèèèèèèèèè If ╬A ╧ ╬C, can you show that ▒┤ ╧ ┤╖?
èèèèèèèèèèèèè (Show sides opposite equal angles are equal.)è
@fig3601.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ▒┤ ╧ ┤╖
Proç: StatementèèèèèèèèèèèèReason
èèè 1. ╬A ╧ ╬Cèèèèèèèèèèè 1. Given
èèè 2. Constuct angle bisecër ┤╗èè2. The angle can be bisected
èèè 3. ╬ABE ╧ ╬CBEèèèèèèèèè 3. Defïition ç angle bisecër
èèè 4. ┤║ ╧ ┤║èèèèèèèèèèè 4. Congruence is reflexive
èèè 5. ΦABE ╧ ΦCBEèèèèèèèèè 5. Congruent by Theorem 3.5.5
èèè 6. ▒┤ ╧ ┤╖èèèèèèèèèèè 6. Correspondïg parts ç
èèèèèèèèèèèèèèèèèèèèèè congruent Φs are congruent
Ç A
3èèèèèèèIf ▒┤ ╧ ┤╖ ╧ ▒╖, can you show that ╬A ╧ ╬B ╧ ╬C?
èèèèèèèèèèèè (Show equilateral triangles are equiangular.)è
@fig3602.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ╬A ╧ ╬B ╧ ╬C
Proç: StatementèèèèèèèèèèèèReason
èèè 1. ▒┤ ╧ ┤╖ ╧ ▒╖èèèèèèèèè1. Given
èèè 2. ╬A ╧ ╬Cèèèèèèèèèèè 2. Theorem 3.6.2 or Problem 1
èèè 3. ╬A ╧ ╬Bèèèèèèèèèèè 3. Theorem 3.6.2 or Problem 1
èèè 4. ╬A ╧ ╬B ╧ ╬Cèèèèèèèèè4. Congruence is transitive
Ç A
4èèèèèèèIf ╬A ╧ ╬B ╧ ╬C, can you show that ▒┤ ╧ ┤╖ ╧ ▒╖?
èèèèèèèèèèèè (Show equiangular triangles are equilateral.)è
@fig3602.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ▒┤ ╧ ┤╖ ╧ ▒╖
Proç: StatementèèèèèèèèèèèèReason
èèè 1. ╬A ╧ ╬B ╧ ╬Cèèèèèèèèè1. Given
èèè 2. ▒┤ ╧ ▒╖èèèèèèèèèèè 2. Theorem 3.6.2 or Problem 2
èèè 3. ┤╖ ╧ ▒╖èèèèèèèèèèè 3. Theorem 3.6.2 or Problem 2
èèè 4. ▒┤ ╧ ┤╖ ╧ ▒╖èèèèèèèèè4. Congruence is transitive
Ç A
5èèèIf ΦABC is isosceles å ┤║ is a median, can you show that
èèèèèèèèè ╬ABE ╧ ╬CBE?è(Show ê median is ê angle bisecër.)è
@fig3601.BMP,35,50,147,74èèèèèèèèA) Yesèèè B) No
ü Show ╬ABE ╧ ╬CBE
Proç: StatementèèèèèèèèèèèèReason
èèè 1. ΦABC is isoscelesèèèèèè 1. Given
èèè 2. ▒┤ ╧ ┤╖èèèèèèèèèèè 2. Defïition ç isosceles
èèè 3. ┤║ is a medianèèèèèèèè3. Given
èèè 4. ▒║ ╧ ║╖èèèèèèèèèèè 4. Defïition ç median
èèè 5. ┤║ ╧ ┤║èèèèèèèèèèè 5. Congruence is reflexive
èèè 6. ΦABE ╧ ΦCBEèèèèèèèèè 6. Congruent by SSS
èèè 7. ╬ABE ╧ ╬CBEèèèèèèèèè 7. Correspondïg parts ç
èèèèèèèèèèèèèèèèèèèèèè congruent Φs
Ç A
6èèèèèèèèèè If ┤║ is an altitude å a median, can you
èèèèèèèèèèèèèèèshow that ΦABC is isosceles?
@fig3601.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ΦABC is isosceles
Proç: StatementèèèèèèèèèèèèReason
èèè 1. ┤║ is an altitudeèèèèèè 1. Given
èèèèèèå a median
èèè 2. ┤║ ß ▒╖èèèèèèèèèèè 2. Defïition ç altitude
èèè 3. ╬AEB, ╬CEB are right ╬sèèè 3. Defïition ç perpendicular
èèè 4. ╬AEB ╧ ╬CEBèèèèèèèèè 4. (14)Angles are congruent
èèè 5. ▒║ ╧ ║╖èèèèèèèèèèè 5. Defïition ç median
èèè 6. ┤║ ╧ ┤║èèèèèèèèèèè 6. Congruence is reflexive
èèè 7. ΦABE ╧ ΦCBEèèèèèèèèè 7. Congruent by SAS
èèè 8. ▒┤ ╧ ┤╖èèèèèèèèèèè 8. Correspondïg parts ç
èèèèèèèèèèèèèèèèèèèèèè congruent Φs
èèè 9. ΦABC is isoscelesèèèèèè 9. Defïition ç isosceles
Ç A
7èèèèè If ΦABC is isosceles å ┤║ is ê altitude ë êè
èèèèèèèèèèvertex angle, can you show ┤║ is ê angle bisecër?
@fig3601.BMP,35,50,147,74èèèèèèèèA) Yesèèè B) No
ü Show ┤║ is ê angle bisecër ç ╬B
Proç: Statementèèèèèèèèèèè Reason
èèè 1. ΦABC is isoscelesèèèèèè1. Given
èèè 2. ▒┤ ╧ ┤╖èèèèèèèèèèè2. Defïition ç isosceles
èèè 3. ┤║ is ê altitudeèèèèè 3. Given
èèè 4. ╬AEB, ╬CEB are right ╬sèèè4. Defïition ç altitude
èèè 5. ╬AEB ╧ ╬CEBèèèèèèèèè5. (14)Right angles are congruent
èèè 6. ╬A ╧ ╬Cèèèèèèèèèèè6. Theorem 3.6.1
èèè 7. ΦABE ╧ ΦCBEèèèèèèèèè7. Theorem 3.5.5
èèè 8. ╬ABE ╧ ╬CBEèèèèèèèèè8. Correspondïg parts ç
èèèèèèèèèèèèèèèèèèèèèècongruent Φs
èèè 9. m╬ABE = m╬CBEèèèèèèèè9. Defïition ç congruence
èèè10. ┤║ bisects ╬Bèèèèèèè 10. Defïition ç angle bisecër
Ç A
8èèèè If ▒┤ ╧ ▒║ å ┤╖ ╧ ║╖, can you show ╬ABC ╧ ╬AEC?è
èèèèèèè
@fig3603.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ╬ABC ╧ ╬AEC
Proç: StatementèèèèèèèèReason
èèè 1. ▒┤ ╧ ▒║èèèèèèè 1. Given
èèè 2. ╬1 ╧ ╬3èèèèèèè 2. ╬s opposite equal sides are congruent
èèè 3. ┤╖ ╧ ║╖èèèèèèè 3. Given
èèè 4. ╬2 ╧ ╬4èèèèèèè 4. ╬s opposite equal sides are congruent
èèè 5. m╬1 = m╬3èèèèèè 5. Defïition ç congruence
èèè 6. m╬2 = m╬4èèèèèè 6. Defïition ç congruence
èèè 7. m╬1 + m╬2èèèèèè 7. Addition axiom for equations
èèèèè= m╬3 + m╬4èèèè
èèè 8. m╬ABE = m╬AECèèèè 8. (12)Angle addition axiom
èèè 9. ╬ABC ╧ ╬AECèèèèè 9. Defïition ç congruenceèèèèèèèèè
Ç A
9èèè If ┤╖ ╧ ║╖ å ╬BPC ╧ ╬EPC, can you show ╬ABC ╧ ╬AEC?è
èèèèèèè
@fig3603.BMP,35,40,147,74èèèèèèèèA) Yesèèè B) No
ü Show ╬ABC ╧ ╬AEC
Proç: StatementèèèèèèèèReason
èèè 1.┤╖ ╧ ║╖èèèèèèè 1. Given
èèè 2. ╬BPC ╧ ╬EPCèèèèè2. Given
èèè 3. ╬2 ╧ ╬4èèèèèèè3. ╬s opposite equal sides are congruent
èèè 4. ΦBCP ╧ ΦECPèèèèè4. Theorem 3.5.5
èèè 5. ┤└ ╧ ║└èèèèèèè5. Correspondïg parts ç congruent Φs
èèè 6. ▒└ ╧ ▒└èèèèèèè6. Congruence is reflexive
èèè 7. ╬APB, ╬APE rt. ╬sèè7. They form pairs with right anglesèèèèèèèèè
èèè 8. ╬APB ╧ ╬APEèèèèè8. Right angles are congruent
èèè 9. ΦABP ╧ ΦAEPèèèèè9. Congruent by SAS
èèè10. ╬1 ╧ ╬3èèèèèè 10. Correspondïg parts ç congruent Φs
èèè11. ╬1 + ╬2 = ╬3 + ╬4è 11. Addition axiom for equationsèèèèè
èèè12. ╬ABC ╧ ╬AECèèèè 12. Def. ç congr. å Seg.add. axiomèèèèèèèèè
Ç A