a: =>xy=8
hay \(\left(x,y\right)\in\left\{\left(1;8\right);\left(8;1\right);\left(2;4\right);\left(4;2\right)\right\}\)
b: =>xy=-10
\(\Leftrightarrow\left(x,y\right)\in\left\{\left(-10;1\right);\left(-5;2\right);\left(-2;5\right);\left(-1;10\right)\right\}\)