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à 3.1èTriangle Defïitions
äèPlease answer ê followïg questions about triangles.
â
èèèèèèèè A triangle is ê union ç three segmentsè
èèèèèèèè joïïg three noncollïear poïts.
éS1 Probably ê most important geometric figure is ê triangle.
Defïition 3.1.1èTRIANGLE:èA triangle is ê union ç three segments
joïïg three noncollïear poïts.
è Every triangle has three sides å three angles.èSome triangles are
identified by ê type ç angles êy have.èFor example, certaï tri-
angles are called acute, obtuse, right, or equiangular.èOêr triangles
are identified by ê lengths ç êir sides.èFor example, certaï tri-
angles are called scalene, isosceles, or equilateral.
Defïition 3.1.2èACUTE TRIANGLE:èAn acute triangle is one ï which all
angles are acute angles.
Defïition 3.1.3èOBTUSE TRIANGLE:èAn obtuse triangle is a triangleè
with one obtuse angle.
Defïition 3.1.4èRIGHT TRIANGLE:èA right triangle is a triangle with
one right angle.èIn a right triangle ê longest side is called ê
hypotenuse, å ê oêr two sides are called ê legs ç ê triangle.
Defïition 3.1.5èEQUIANGULAR TRIANGLE:èAn equiangular triangle is a
triangle with all angles equal.
Defïition 3.1.6èSCALENE TRIANGLE:èA scalene triangle is a triangle
with no two sides congruent.
Defïition 3.1.7èISOSCELESE TRIANGLE:èAn isosceles triangle is a tri-
angle with two equal sides.èThe third side is called ê base.
Defïition 3.1.8èEQUILATERAL TRIANGLE:èA triangle is an equilateral
triangle if all three sides are equal ï length.
èèèèèèèèèèèèèèèèèèèè This figure shows ΦABC.èThis
èèèèèèèèèèèèèèèèèèèè triangle has three sides å
èèèèèèèèèèèèèèèèèèèè three angles, ▒┤, ┤╖, ╖▒, ╬A,
èèèèèèèèèèèèèèèèèèèè ╬B, å ╬C.èIn this figure
èèèèèèèèèèèèèèèèèèèè we would say that ╬A is oppo-
èèèèèèèèèèèèèèèèèèèè site side ┤╖, ╬B is oppositeè
@fig3101.BMP,35,220,147,74èèèèèèè side ▒╖, å ╬C is opposite
side ▒┤.èAlso, we would say that ╬A is ïcluded by sides ▒┤ å ▒╖,
å side ▒┤ is ïcluded by ╬A å ╬B.èWe would refer ë A, B, å C
as ê vertices.èWe would also say that x is ïterior å y is exterior
ë ê triangle.
è Some triangles can be described by more han one term.èFor example,
a right triangle with all sides ç different lengths could be called a
right, scalene triangle.èA right triangle with two equal sides could
be called an isosceles, right triangle.èOêr examples are equilateral,
acute triangle å isosceles, obtuse triangle.
1èèèèè What kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèA) Isosceles, right triangle
èèèèèèèèèèèèèèèèèèèèèèB) Scalene, right triangle
èèèèèèèèèèèèèèèèèèèèèèC) Obtuse, right triangle
èèèèèèèèèèèèèèèèèèèèèèD) None
@fig3102.BMP,35,40,147,74è
ü
èèèèèèèèè ΦABC is a scalene, right triangle.
Ç Bèèèèè
2èèèèèè Name ê hypotenuse ç ΦABC.è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ▒┤
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ▒╖
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ┤╖
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3102.BMP,35,40,147,74è
ü
èèèèèèèèèèèèThe hypotenuse is side ▒┤.
Ç Aè
3èèèèèèèèè Name ê legs ç ΦABC.
èèèèèèèèèèèèèèèèèA)èa å c
èèèèèèèèèèèèèèèèèB)èc å b
èèèèèèèèèèèèèèèèèC)èb å a
èèèèèèèèèèèèèèèèèD)èNone ç êse
@fig3102.bmp,35,40,147,74èèèè
ü
èèèèèèèèèèThe legs are sides a å b.
Ç C
4èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèèè A) Obtuse triangleè
èèèèèèèèèèèèèèèèèèèèèèèèè B) Scalene triangle
èèèèèèèèèèèèèèèèèèèèèèèèè C) Isosceles triangle
èèèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3103.BMP,35,40,147,74è
ü
èèèèèèèèèè ΦABC is an isosceles triangle.
Ç Cèèèèè
5èèèèèèName ê vertex angle ç ΦABC.è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ╬Aè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ╬B
èèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ╬C
èèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3103.BMP,35,40,147,74è
ü
èèèèèèèThe vertex angle ç an isosceles triangle is êè
èèèèèèèangle ïcluded by ê two equal sides.è╬Aèè
Ç Aèèèèè
6èèèèèèName ê base angles ç ΦABC.è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ╬A å ╬Bè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ╬B å ╬C
èèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ╬A å ╬C
èèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3103.BMP,35,40,147,74è
ü
èèèèèèèèèè The base angles are ╬B å ╬C.è
èèèèèèè
Ç Bèèèèè
7èèèèèèèèName ê legs ç ΦABC.è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) a å cè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) b å a
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) b å c
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3103.BMP,35,40,147,74è
ü
èèè The legs ç an isosceles triangle are ê two equal sides.èèèèèèèè
Ç Cèèèèè
8èèèèè What kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèè A) Equilateral triangleèè
èèèèèèèèèèèèèèèèèèèèèèèè B) Scalene triangle
èèèèèèèèèèèèèèèèèèèèèèèè C) Obtuse triangle
èèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3104.BMP,35,40,147,74è
ü
èèèèèèèèèè ΦABC is an equilateral triangle.èèèèèèèè
Ç A
9èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèèèè A) Right triangleèè
èèèèèèèèèèèèèèèèèèèèèèèèèè B) Obtuse triangle
èèèèèèèèèèèèèèèèèèèèèèèèèè C) Acute triangle
èèèèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3104.BMP,35,40,147,74è
ü
èèèèèèèèèèèèΦABC is an acute triangle.èèèèèèèè
Ç Cèèèèè
10èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèè A) Scalene triangleèè
èèèèèèèèèèèèèèèèèèèèèèèè B) Equiangular triangle
èèèèèèèèèèèèèèèèèèèèèèèè C) Right triangle
èèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3104.BMP,35,40,147,74è
ü
èèèèèèèèèè ΦABC is an equiangular triangle.èèèèèèèè
Ç Bèèèèè
11èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèè A) Isosceles triangleèè
èèèèèèèèèèèèèèèèèèèèèèèè B) Scalene triangle
èèèèèèèèèèèèèèèèèèèèèèèè C) Acute triangle
èèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3105.BMP,35,40,147,74è
ü
èèèèèèèèèèèΦABC is an isosceles triangle.èèèèèèèè
Ç Aèèèèè
12èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèè A) Acute triangleèè
èèèèèèèèèèèèèèèèèèèèèèèè B) Right triangle
èèèèèèèèèèèèèèèèèèèèèèèè C) Obtuse triangle
èèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3105.BMP,35,40,147,74è
ü
èèèèèèèèèèèèΦABC is an obtuse triangle.èèèèèèèè
Ç Cèèèèè
13èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèè A) Scalene triangleèè
èèèèèèèèèèèèèèèèèèèèèèèè B) Acute triangle
èèèèèèèèèèèèèèèèèèèèèèèè C) Isosceles triangle
èèèèèèèèèèèèèèèèèèèèèèèè D) None
@fig3102.BMP,35,40,147,74è
ü
èèèèèèèèèèè ΦABC is a scalene triangle.èèèèèèèè
Ç Aèèèèè
14èèèèèèWhat kïd ç triangle is ΦABC?è
èèèèèèèèèèèèèèèèèèèèèèèèèèA) Obtuse triangleèè
èèèèèèèèèèèèèèèèèèèèèèèèèèB) Right triangle
èèèèèèèèèèèèèèèèèèèèèèèèèèC) Acute triangle
èèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3102.BMP,35,40,147,74è
ü
èèèèèèèèèèèè ΦABC is a right triangle.èèèèèèèè
Ç Bèèèèè
15èèèWhat kïd ç triangle is ΦABC?è a ƒ b ƒ cè
èèèèèèèèèèèèèèèèèèèA) Right, obtuse triangleèè
èèèèèèèèèèèèèèèèèèèB) Acute, scalene triangle
èèèèèèèèèèèèèèèèèèèC) Isosceles, equilateral triangle
èèèèèèèèèèèèèèèèèèèD) None
@fig3106.BMP,35,40,147,74è
ü
èèèèèèèèè ΦABC is an acute, scalene triangle.èèèèèèèè
Ç Bèèèèè
16èèèèè What side is ïcluded by ╬A å ╬C?è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ┤╖èè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ▒╖
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ▒┤
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3106.BMP,35,40,147,74è
ü
èèèèèèèèèè Side ▒╖ is ïcluded by ╬A å ╬C.èèèèèèèèèèèèèèèèè
Ç Bèèèèè
17èèèè What angle is ïcluded by ▒┤ å ┤╖?è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ╬Bèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ╬C
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ╬A
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3106.BMP,35,40,147,74è
ü
èèèèèèèèèèè╬B is ïcluded by ▒┤ å ┤╖.èèèèèèèèèèèèèèèèè
Ç Aèèèèè
18èèèèèèè What side is opposite ╬C?è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ▒╖èè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ┤╖
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ▒┤
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3106.BMP,35,40,147,74è
ü
èèèèèèèèèèèèèSide ▒┤ is opposite ╬C.èèèèèèèèèèèèèèèèè
Ç Cèèèèè
19èèèèèèWhat angle is opposite side ┤╖?è
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèA) ╬Bèè
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèB) ╬A
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèC) ╬C
èèèèèèèèèèèèèèèèèèèèèèèèèèèèèèD) None
@fig3106.BMP,35,40,147,74è
ü
èèèèèèèèèèèè ╬A is opposite side ┤╖.èèèèèèèèèèèèèèèèè
Ç Bèèèèè