ABC . C- . CD=6. BD-AD=5 .
: ABC.
.
1.
CD2+BD2=BC2
CD2+AD2=AC2
CD=6
36+BD2=BC2
36+AD2=AC2
BD-AD=5,
BD = AD+5,
36+(AD+5)2=BC2
36+AD2=AC2
. , - . :
36+36+(AD+5)2+AD2=AC2+BC2
72+(AD+5)2+AD2=AC2+BC2
2. , , , :
AC2+BC2=AB2
AB=BD+AD, :
AC2+BC2=(AD+BD)2
BD-AD=5, BD = AD+5,
AC2+BC2=(AD+AD+5)2
3. , . :
72+(AD+5)2+AD2=AC2+BC2
AC2+BC2=(AD+AD+5)2
AC2+BC2 . , .
72+(AD+5)2+AD2=(AD+AD+5)2
72+AD2+10AD+25+AD2=4AD2+20AD+25
-2AD2-10AD+72=0
D=676, , :
1=-3,5
x2=4
, .
AD=4
BD = AD + 5 = 9
AB = BD + AD = 4 + 9 = 13
:
AC = (52)
BC = (117).
.
30 7 .
.
180 .
.
( ) 7, ( , - ), , 7 + 30.
:
+ 7 + (7 + 30) = 180
15 + 30 = 180
15 = 150
=10
. 7 = 70, 7+30 = 100
: 10, 70, 100
.
CD. BCD 65 .
.
, 180 , :
∠A + ∠B + ∠C = 180
- ,
65 + ∠B + 90 = 180
B = 25
, CD - , BCD - ,
∠CBD + ∠CDB + ∠BCD = 180
25 + 90 + ∠BCD =180
∠BCD =65
: 65
. . , - . " " sqrt(), sqrt - , . √
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. , - . " ".
:
:
a, b, c - ,
r -
R -
h - ,
p - , 1/2
, 1 ,
2 , (. ).
. .
5 6 . 60 . .
.
S=1/2 ab sin C
S=1/2 *5*6*sin60
S=15√3 / 2
- sqrt .
: 7,5 √3
3.
.
:
S = 1/4 sqrt((a + b + c)(b + c - a)(a + c - b)(a + b -c))
a = b = c :
S = √3 / 4 * a2
S = √3 / 4 * 32
S = 9 √3 / 4
: 9 √3 / 4.
, 4 ?
.
.
S = 1/4 sqrt((a + b + c)(b + c - a)(a + c - b)(a + b -c))
4 ,
S2 = 1/4 sqrt((4a + 4b + 4c)(4b + 4c - 4a)(4a + 4c - 4b)(4a + 4b -4c))
, 4 - , .
S2 = 1/4 sqrt(4 * 4 * 4 * 4 (a + b + c)(b + c - a)(a + c - b)(a + b -c))
S2 = 1/4 sqrt(256 (a + b + c)(b + c - a)(a + c - b)(a + b -c))
S2 = 16 * 1/4 sqrt((a + b + c)(b + c - a)(a + c - b)(a + b -c))
,
S2 / S = 16
: 16
.
A ABC BC BK = 8 KC = 18 . AC, AB = 12 .
.
:
, .
:
BK/KC = AB/AC
8/18=12/x
x=27
.
, AD ABC BC, AB=6 BC=7 AC=8.
.
:
, .
:
BD/DC = AB/AC
BD/DC = 6/8
BD = x, DC = 7 - x
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x / (7 - x) = 6/8
8x = 42 - 6x
14x = 42
x =3
DC = 4
: BD = 3, DC = 4