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
10x^2+x-2=0
D=1-4*10*(-2)=1+80=81
√D=9
x1=(-1+9)/20=8/20=0,4
x2=(-1-9)/20=-10/20=-0,5
10x^2+x-2=10*(x-0,4)*(x+0,5)
2) знаменатель
x^2+2,1x-1=0
D=2,1^2+4=4,41+4=8,41
√D=2,9
x1=(-2,1+2,9)/2=0,8/2=0,4
x2=(-2,1-2,9)/2= - 5/2= - 2,5
x^2+2,1x-1=(x-0,4)*(x+2,5)
(10x^2+x-2)/(x^2+2,1x-1)=10*(x-0,4)*(x+0,5)/(x-0,4)*(x+2,5) = =10*(x+0,5)/(x+2,5) = (10x+5)/(x+2,5)