. . , . , - .
ABC KLMN. M AC, N AC, K AB, L BC. , AC a, BD, B h.
.
x. , BD E.
BD = BE + ED
ED ,
h = BE + x
BE = h - x
ABC BKL , , . . :
KL / AC = BE / BD
KL - ,
x / a = (h - x) / h
xh = a (h - x)
xh = ah - ax
xh + ax = ah
x (h + a) = ah
x = ah / (h + a)
: ah / (h + a)
ABC AB D, , BD:BA=1:3. , AC D, BC D1. , DBD1 ABC.
.
: " ".
, D, BC D1 AC, DD1 , AC.
, " ". :
BD / AD = BD1 / D1C
" , ".
DBD1 ABC . , .
. ( ). , - . " " sqrt(), sqrt - , .
.
1 . .
.
, +1, +2.
:
x2 + (x + 1)2 = (x + 2)2
x2 + (x + 1)2 = (x + 2)2
x2 + x2 + 2x + 1 = x2 + 4x +4
2x2 + 2x +1 - x2 - 4x -4 = 0
x2 - 2x - 3 = 0
|
|
D = 16
x1 = 3
x2 = -1 ( )
S = 1/2 ab = 1/2 * 3 * 4 = 6 2.
S = 1/4 sqrt((a + b + c) (a + b - c) (a - b + c) (b + c - a))
S = 1/4 sqrt((3 + 4 + 5) (3 + 4 - 5) (3 - 4 + 5) (4 + 5 - 3))
S = 1/4 sqrt(12 * 2 * 4 * 6)
S = 1/4 √ 576 = 6 2.
: 6 2
.
52 73. .
.
. a b. , :
a2 = 73 - 4b2
b2 + 4(73 - 4b2) = 52
b2 + 292 - 16b2 = 52
15b2 = 240
b2 = 16
b = 4
, 2 = 73 - 4 * 16 = 9, = 3
, (2a 2b) 8 6 .
S = 1/2 8*6 = 24 2.
: 24 2.
.
90, 3 , 2 . tg
.
tg A = BC /AC
BC = AC + 2
AC = 3
tg A = 5 / 3