1 * x + 3ix + 2y - 5iy = 7 + i;
x + 2y = 7; 3x + 6y = 21;
i: 3x - 5y = 1;
11y = 20;
y = 20/11;
x + 40/11 = 7;
x = 37/11; y = 20/11.
(х-10)(х+30)-(х-20)(х+20)=40
х²+30х-10х-300-х²+400-40=0
20х+60=0
20х=-60
х=-60:20
х=-3
проверка
(-3-10)(-3+30)-(-3-20)(-3+20)=40
(-13)*27-(-23)*17=40
-251+396=40
40=40