x+20y+10xy=40
x+20y-10xy=-8
(x+20y+10xy)-(x+20y-10xy)=40-(-8)
x+20y+10xy-x-20y+10xy=40+8
20xy=48
xy=2.4
x+20y+24=40
x+20y=16
y=2.4/x
x+20*2.4/x=16
x+48/x=16
(x+48/x)*x=16*x
x^2+48=16x
x^2-16x+48=0
(x-4)(x-12)=0
x1=4
x2=12
y1=2.4/4=0.6
y2=2.4/12=0.2
Проверка:
4+20*0.6+10*4*0.6=40
4+12+24=40
40=40
4+20*0.6-10*4*0.6=-8
4+12-24=-8
-8=-8
12+20*0.2+10*12*0.2=40
12+4+24=40
12+4-24=-8
x+20y+10xy=40
x+20y-10xy=-8
x+20y+10xy=40
(x+20y+10xy)-(x+20y-10xy)=40-(-8)
x+20y+10xy=40
x+20y+10xy-x-20y+10xy=40+8
x+20y+10xy=40
20xy=48
x+20y+10xy=40
xy=2.4
x+20y+24=40
xy=2.4
x+20y=16
y=2.4/x
x+20*2.4/x=16
y=2.4/x
x+48/x=16
y=2.4/x
(x+48/x)*x=16*x
y=2.4/x
x^2+48=16x
y=2.4/x
x^2-16x+48=0
y=2.4/x
(x-4)(x-12)=0
y=2.4/x
x1=4
x2=12
y1=2.4/4=0.6
y2=2.4/12=0.2
Проверка:
x1=4
y1=2.4/4=0.6
x+20y+10xy=40
4+20*0.6+10*4*0.6=40
4+12+24=40
40=40
x+20y-10xy=-8
4+20*0.6-10*4*0.6=-8
4+12-24=-8
-8=-8
x2=12
y2=2.4/12=0.2
x+20y+10xy=40
12+20*0.2+10*12*0.2=40
12+4+24=40
40=40
x+20y-10xy=-8
12+4-24=-8
-8=-8
5х+2у=0 3х+2у=-5 3х+у=7
у=1-2х х-=7-5у 2х+3у=1
5х+2у=0 3х+2у=-5 у=7-3х
5х+2(1-2х)=0 3(7-5у)+2у=-5 2х+3(7-3х)=1
5х+2-4х=0 21-15у+2у=-5 2х+21-9х=1
х=-2 -13у=-5-21 -7х=-20
у=2 х=7/20
х=-2 х=-3 х=7/20
у=5 у=2 у=21/20