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Rectangles,
Rhombu s e s , and
Squares
Pembahasan soal-soal
Kelompok 3
Annisa Luthfi Fadhilah Ma’ruf ; Rosyida Khikmawati ; Rizqi Dwi
Maharani ; Nadiatul Khikmah
No 36 Page 287
Given : WXYZ is a square
AW=BX=CY=DZ
Prove : ABCD is a square
Answer
Statements
Reasons
AW  BX
Given
<AWB  <BXC
Supplementary angle
BW

Addition of equal segment
CX
∆BAW  ∆CBX
BA
BA


SAS Postulate
CPCTC
CB
CB

CD
ABCD is a square

DA
CP
Definition of square
No 32 Page 286
Given : WXYZ is a rhombus
R is the midpoint of WV
T is the midpoint of VY
S is a point of VZ
Prove : ∆ RST is isosceles
Answer
Statements
Reasons
 YZ
<WZV  <YZV
Definition of rhombus
WX
ZV

ZV
∆WZV  ∆YZV
RV

∆RVS
SV

∆RVS
SR

∆RST
∆TVS
ST
SAS postulate
Perpendicular bisector
Reflexive
SV

Reflexive
Given
TV

Definition of angle bisector
∆TVS
SAS postulate
CPCTC
Isosceles triangle
No 30 Page 295
Prove that AB││DE
Answer
Plan : Draw AE
Statements
BE

<BEA
EA

Definition of regular octagon
DA

Reasons
<DAE
AE
∆ABE  ∆EDA
AB ││ DE
Alternate interior angle
Reflexive
SAS Postulate
Theorem 5-2
(If two lines are cut by a transversal and a
pair of alternate interior angles are
congruent, then the lines are parallel)
No 29 Page 295
Inscribed in a regular octagon is a star polygon.
Find m<ABC. Prove that your answer is correct.
Answer
Plan : Draw XA and YB intersecting at T
Statements
Reasons
XY  YX
Definition of regular octagon
YB  XA
CPCTC
XB  AY
Definition of regular octagon
∆XAB  ∆YBA
SSS Postulate
<XAB  <YBA
CPCTC
TB  TA
Side opposite congruent triangle
TX  TY
Substraction
∆BTA and ∆XTY
Are isosceles triangle
<TXY  <TYX ; <TBA  <TAB
Base angles
<XTY  <ATB
Vertical angles
<TXY  <TAB
Substraction
………Answer
Statements
Reasons
m<XBA + m<BXY = 180
<XBA is suplementary to <BXY
m<BXY=135
Theorem 8-15
(The measure of an angle of a regular
pentagon of n sides is (n-2)/n x 180)
m<XBA = m<EBC = 45
Same as above pattern
m<ABC = 45
m<ABC = 135-2(45)
=45
No 16 Page 291
Given : ∆ABC is isosceles with AB  AC,
<AED  <B
Prove : BCDE is a trapezoid with BE  CD
Answer
Statements
<AED

<B
ED ││ BC
BCDE is a trapezoid
Reasons
Given
Theorem 5-1
(if two lines are cut by a transversal and a
pair of corresponding angles are
congruent, then the line are parallel)
Definition of trapezoid
(Trapezoid is a quadrilateral with exactly
one of parallel side)
No 9 Page 298
The figures shown are two overlapping
rectangles. Find the sum, a+b+c+d.
Answer


Based on the figures shown that a,b,c,d is the
exterior angles of a poygon that built from two
overlapping rectangles.
So, the sum a+b+c+d=360 (theorem 8-16)
(The sum of the measures of the exterior angles of
an polygon, one each vertex, is 360)
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