内容正文:
书
《
!"#
》
$%&'(
)
、
!"
1 2 3 4 5 6 7 8 9 10
#$
B A B D B A B B C D
*
、11.AE; 12.22; 13.10°;
14.540°
!
360°
!
180°.
+
、15.
"#∠A=46°,∠C=74°,$%∠ABC=
180°-∠A-∠C=60°."# BD&' ∠ABC,$%
∠ABD=12∠ABC=30°.$%∠BDC=∠A+∠ABD
=76°.
16.(1)3;
(2)
"#()*+,-./01234
:3,5,7;3,
7,7;3,7,9,
$%567801,0*,9#
:3+5+7
+3+7+7+3+7+9=51(
%&
),51×8=408(
'
).
:
:
;<=>
408
?@ABCD
.
17.
E
AC=x,
F
AB=2x.
"#
BD
G△ABCH ACIJ,HK,$% AD=
CD=12x.LMN,O2x+
1
2x=30.POx=12.$%
CD=6,AB=24.
$%
BC=20-6=14.
18.
EQI/,RST.#α°,FUVWX,Y.
#
(3α+20)°.
LMN
,
O
(3α+20)+α=180.
POα=40,Z7SQI/,[ST.#40°.
"#QI/,T.\#
360°,
$%7SQI/,
I]#
:360°÷40°=9.
$%VY.\#
:(9-2)×
180°=1260°.
19.
"#
BE
&'∠CBD,$%∠CBD=2∠CBE.
^△CBDH,∠BDC=180°-∠CBD-∠C.
_"#
90°+∠C=∠BDC,
$%
180°-∠CBD-∠C=90°+∠C.
$%
2∠C+∠CBD=90°,Z2∠C+2∠CBE=
90°.
$%∠C+∠CBE=45°=∠AEB.
"#
EB⊥AB,$%∠EBA=90°.
$%∠A=90°-∠AEB=45°.
《
!"#
》
$%,'(
)
、
!"
1 2 3 4 5 6 7 8 9 10
#$
B C A C D C B C C C
*
、11.65°; 12.27; 13.116°;
14.42°
!
84°
!
92°.
+
、15.(1)
"#
AB=32AC,AC=10cm,$%AB=
15cm.
_"#△ABC,`9#33cm,$%BC=8cm."
#
AD
G
BC
IJ,HK
,
$%
BD=12BC=4cm.
(2)
ab
.
cLde
:
"#
AB=32AC,AC=12cm,$%AB=18cm._
"#△ABC,`9#33cm,$%BC=3cm."#AC
+BC=15<AB,
$%abfg-./
.
$%abhi
DC
,9
.
16.(1)
"#∠ACB=90°,∠A=40°,$%∠CBD
=∠ACB+∠A=130°."#BEG∠CBD,&'K,
$%∠CBE= 12∠CBD=65°.
(2)
"#∠ACB=90°,$%∠BCE=90°._"#
∠CBE=65°,$%∠CEB=90°-∠CBE=25°."#
∠F=25°,$%∠F=∠CEB.$%BE∥DF.
17.(1)
LMN
,
O$jk,lKmnfgRST
.G
20°
,mQI/
.
opQI/,T.\qr
360°,
sO7SQI/,I]#
:360°÷20°=18.
$%tu
Rvwx
:18×10=180(
&
).
(2)
7SQI/,Y.\G
:(18-2)×180°=
2880°.
18.
"#
AE,BF
G△ABC,.&'K,$%∠BAC
=2∠OAB,∠ABC=2∠OBA.$%∠BAC+∠ABC=
2(∠OAB+∠OBA)=2(180°-∠AOB)."#∠AOB
=125°,
$%∠BAC+∠ABC=110°.$%∠C=180°
-(∠BAC+∠ABC)=70°."#ADG△ABC,y,$
%∠ADC=90°.$%∠DAC=90°-∠C=20°.
19.(1)
"#∠B=∠C=45°,$%∠BAC=180°
-(∠B+∠C)=90°."#∠BAD=60°,$%∠DAC
=∠BAC-∠BAD=30°.$%∠ADC=180°-∠DAC
-∠C=105°."# ∠ADE=∠AED,$% ∠ADE=
∠AED=75°.$%∠CDE=∠ADC-∠ADE=30°.
(2)∠BAD=2∠CDE.cLde:
E∠BAD=x,F∠DAC=∠BAC-∠BAD=90°
-x.
$%∠ADC=180°-∠DAC-∠C=45°+x.
"#∠ADE=∠AED,
$%∠ADE=∠AED=45°+12x.
$%∠CDE=∠ADC-∠ADE= 12x.
$%∠BAD=2∠CDE.
(3)
E∠BAD=y.
"#∠B=∠C,
$%∠DAC=∠BAC-∠BAD=180°-2∠C-y.
$%∠A