a: =>ab-3b-a=5
=>a(b-1)-3b+3=8
=>(b-1)(a-3)=8
=>\(\left(a-3;b-1\right)\in\left\{\left(1;8\right);\left(8;1\right);\left(-1;-8\right);\left(-8;-1\right);\left(2;4\right);\left(4;2\right);\left(-2;-4\right);\left(-4;-2\right)\right\}\)
=>\(\left(a,b\right)\in\left\{\left(4;9\right);\left(11;2\right);\left(2;-7\right);\left(-5;0\right);\left(5;5\right);\left(7;3\right);\left(1;-3\right);\left(-1;-1\right)\right\}\)
b: =>ab-3b-3=5
=>b(a-3)=8
=>\(\left(a-3;b\right)\in\left\{\left(1;8\right);\left(8;1\right);\left(-1;-8\right);\left(-8;-1\right);\left(2;4\right);\left(4;2\right);\left(-2;-4\right);\left(-4;-2\right)\right\}\)
=>\(\left(a,b\right)\in\left\{\left(4;8\right);\left(11;1\right);\left(2;-8\right);\left(-5;-1\right);\left(5;4\right);\left(7;2\right);\left(1;-4\right);\left(-1;-2\right)\right\}\)