1) 18/x_46/(x-5) =1;
18(x-5)-6x=x(x-5) ;
x² +23x+90=0 ⇒ x₁ = 5, x₂ =18.
2) { 7x - y =5; { y =7x - 5;
{xy=18; {{xy=18;
x(7x-5)=18;
7x² -5x -18=0 ⇒ x₁= - 9/7 ; x₂ =2.
y₁ =7x₁ - 5=7*(-9/7) - 5 = -14₁
y₂ =7x₂ -5 =7*2 -5=9;
ответ : { (-9/7;-14) ;(2; 9) }
3) 28/(x-1) + 16/(x+1)=3 ;
28(x+1) +16(x-1) =3(x-1)(x+1);
3x² -44 x - 15=0;
x= (22 +sqrt(484 45)/3=(22+23)/3 =45/3=15 .