\(ab+2a-3b-6=1\)
\(\Leftrightarrow a\left(b+2\right)-3\left(b+2\right)=1\)
\(\Leftrightarrow\left(a-3\right)\left(b+2\right)=1=1.1=\left(-1\right).\left(-1\right)\)
\(\Rightarrow\left(a;b\right)=\left(4;-1\right);\left(2;-3\right)\)
b/ \(A=\frac{5\left(x^2-x+1\right)+x^2-6x+9}{x^2-x+1}=5+\frac{\left(x-3\right)^2}{\left(x-\frac{1}{2}\right)^2+\frac{3}{4}}\ge5\)
\(A_{min}=5\) khi \(x=3\)