Question

система x^2-xy-y^2=19 x-y=7

Answer 1

$left { {{ x^{2} -xy- y^{2} =19} atop {x-y=7}} right. left { {{ x^{2}-xy- y^{2} =19} atop {x=7+y}} right. left { {{ (7-y)^{2}-(7-y)y- y^{2}=19 } atop {x=7+y}} right.$
49+14y+y²-7y-y²-19=0
30+7y-y²=0
D=49+4*30=120+49=169
√D=√169=13
$y_{1} = frac{7+13}{2} y_{1} =10 y_{2}= frac{7-13}{2} y_{2}=-3$
, тогда 
$x_{1}=7+10 x_{1}=17 x_{2}=7-(-3) x_{2}=10$
Ответ (17;10) и (10;-3)