a: (x+5)(y-3)=15
\(\Leftrightarrow\left(x+5;y-3\right)\in\left\{\left(1;15\right);\left(15;1\right);\left(-1;-15\right);\left(-15;-1\right);\left(3;5\right);\left(5;3\right);\left(-3;-5\right);\left(-5;-3\right)\right\}\)
\(\Leftrightarrow\left(x,y\right)\in\left\{\left(-4;18\right);\left(10;4\right);\left(-6;-12\right);\left(-20;2\right);\left(-2;8\right);\left(0;6\right);\left(-8;-2\right);\left(-10;0\right)\right\}\)
b: \(\Leftrightarrow x+7⋮x+2\)
\(\Leftrightarrow x+2+5⋮x+2\)
\(\Leftrightarrow x+2\in\left\{1;-1;5;-5\right\}\)
hay \(x\in\left\{-1;-3;3;-7\right\}\)
c: \(\Leftrightarrow x+5⋮x-1\)
\(\Leftrightarrow x-1+6⋮x-1\)
\(\Leftrightarrow x-1\in\left\{1;-1;2;-2;3;-3;6;-6\right\}\)
hay \(x\in\left\{2;0;3;-1;4;-2;7;-5\right\}\)
