. ( - ). , . , - . √.
" " , :
, .
.
.
144 2, 14 . .
.
- .
, √144 = 12 .
√(122 + 122) = √288 = 12√2
. , :
√((12√2)2 + 142) = 22
: 22
, 5 , 4 .
.
, ( a) :
a2 + a2 = 52
2a2 = 25
a = √12,5
( h) :
h2 + 12,5 = 42
h2 + 12,5 = 16
h2 = 3,5
h = √3,5
S = 2a2 + 4ah
S = 25 + 4√12,5 * √3,5
S = 25 + 4√43,75
S = 25 + 4√(175/4)
S = 25 + 4√(7*25/4)
S = 25 + 10√7 ≈ 51,46 2.
: 25 + 10√7 ≈ 51,46 2.
. ( ). , . , - . √.
ABCD A1B1C1D1 ABCD 4 4√3 , 30 . AC1 60 . .
.
180 , B D. 180 - 30 = 150 .
AC, , ACD C 150 .
, d, a b. , 150 cos(150) = -√3 / 2. :
d2 = a2 + b2 - 2abcos(150)
d2 = 16 + 48 - 2 * 4 * 4√3 * (-√3 / 2) = 112
d = 4√7
AC = 4√7
|
|
, . , AC1 (AC1) , ( - ) . ∠C1AC 60 . ∠C1AC , tg (∠C1AC) = C1 / AC. , 60 tg 60 = √3.
, C1 = AC tg (∠C1AC)
C1 = 4√7 * tg60
C1 = 4√21
, :
S = 2ha + 2hb
S = 2 * 4 √21 * 4 √3 + 2 * 4 √21 * 4 = 96√7 + 16√21 ≈ 327,31
: 96√7 + 16√21 ≈ 327,31
.
- 120 . 8 60 . .
.
AC1 AA1 60 , , C1AC 90 - 60 = 30 .
cos 30 = AC / AC1 = √3 / 2
AC / AC1 = √3 / 2
AC / 8 = √3 / 2
2AC = 8√3
AC = 4√3
ADC 120 , BAD 60 . ( 180(n-2) = 360 , ).
, BAD 60 , ABD BDC- . ( ABCD - , , , (180 - 60) / 2 = 60 . , - ).
. , AO = AC / 2 = 4√3 / 2 = 2√3
ABD , AO . ,
h = √3 / 2,
√3 / 2 = 2√3
= 4
, BD = 4 , DD1 = 4 , :
BD12 = 4 + 4
, 4 , , ABD BDC- , 4 .
, , , AC1 = 8 , C1AC = 30 . sin 30 = C1C / AC1 = 1/2
C1C / 8 = 1/2
C1C = 4
BD = 4 ( ), D1D = 4 ( ), :
BD12 = DD12 + BD2
BD12 = 42 + 42
BD12 = 32
BD1 = 4√2
: - 4 , 4√2 .
. ( - ). , . , - . √.
, :
, .
|
|
. . , 8 , 5 .
.
( F) , ( AC) AFC. AF = AC . , AF - .
, AFC : AF=FC=5 , AC = 8 .
AFC , . K.
, . , :
FK2 + (AC/2)2 = FC2
FK2 + 16 = 25
FK2 = 9
FK = 3
: 3 .
ABCD ABCDA1B1C1D1 DB1 = 6 , DB = 5 , BC1 = 4 .
.
( , , ) .
BB1 DBB1
BB1 = √(B1D2 - BD2)
BB1 = √(36 - 25) = 3
1 = BB1 = 3
BC1C
BC = √(BC12 - C1C2)
BC = √(16 - 9) = √7
BCD CD
CD = √(BD2 - BC2)
CD = √(25 - 7) = √18 = 3√2
:
S = BC * CD = √7 * 3√2 = 3√14
: 3√14
( 2)
. ( - ). , - . " " sqrt(), sqrt - , . "√"
.
- . , P Q
.
P = hd1,
h -
d1 -
Q= hd2,
h -
d2 -
,
d1 = P / h
d2 = Q / h
S = 4ah,
a -
h -
a = sqrt((d1 / 2)2 + (d2 / 2)2)
a = sqrt(d12 / 4 + d22 / 4)
a = sqrt(d12 + d22) / 2
S = 4ah
S = 4h sqrt(d12 + d22) / 2
S = 2h sqrt(d12 + d22)
d1 = P / h
d2 = Q / h
S = 2h sqrt((P / h)2 + (Q / h)2)
S = 2h sqrt(P 2 + Q2) / h
S = 2 sqrt(P 2 + Q2)
: S = 2 √(P 2 + Q2)
.