X+Z=2Y+4
Y^2=ZX
ZX+9X=Y^2+4Y+4
XZ+9X=ZX+4Y+4
4Y=9X-4 2Y=4,5X-2
X+Z=4,5X-2+4=4,5X+2
Z=3,5X+2
14X^2+8X=(4,5X-2)^2
14X^2+8X=4,5^2X^2+4-18X
6,25X^2-26X+4=0
13+-SQRT(169-25)/6,25
(13+-12)/6,25
X1=4
X2=4/25
18(20-x)+20(x+20)=2(x+20)(20-x) ОДЗ ч/=-20 x/=20