Hệ phương trình $\left\{ {\begin{array}{*{20}{c}}{x.y + x + y = 11}\\{{x^2}y + x{y^2} = 30}\end{array}} \right.$

$\left( {15;6} \right),\left( {6;15} \right).$

$\left( {-15;-6} \right),\left( {-6;-15} \right).$      

$\left( {15;{\rm{ }}6} \right),\left( {-6;-15} \right).$  

$\left( {15;6} \right),\left( {6;15} \right),\left( {-15;-6} \right),\left( {-6;-15} \right).$

${S^2}-P < 0.$

${S^2}-P \ge 0.$

${S^2}-4P < 0.$

${S^2}-4P \ge 0.$

$m = \sqrt 2 .$

$m =  - \sqrt 2 .$

$m = \sqrt 2$hoặc $m =  - \sqrt 2 .$

$m$ tùy ý

$x =  - 3;y = 2.$

$x = 2;y =  - 1.$

$x = 4;y =  - 3.$

$x = - 4;y = 3.$

$\left( {2;1} \right).$

$\left( {1;2} \right).$

$\left( {2;1} \right),\left( {1;2} \right).$

Vô nghiệm

$\left( {3;2} \right),\left( {2;3} \right).$

$\left( { - 3; - 7} \right),\left( { - 7; - 3} \right).$

$\left( {3;2} \right);\left( { - 3; - 7} \right).$

$\left( {3;2} \right),\left( {2;3} \right),\left( { - 3; - 7} \right),\left( { - 7; - 3} \right).$