Question

решите систему уравнений:
{3(x+y)-xy=-1  
{4xy+x+y=-9

Answer 1

$-xy+3(x+y)=-1\ 4xy+x+y=-9\\ -4xy+12(x+y)=-4\ 4xy+x+y=-9\\ 13(x+y)=-13\ x+y=-1\ x=-1-y\\ -3+(1+y)y=-1\ y^2+y-2=0\ D=1+4*1*2=3^2\ y=1;-2\ x=-2;1$