\(Dk...n\ne2\Leftrightarrow D=\frac{n^2+3n-21}{2-n}\)
n^2-3n=n(n-3)=0=> n=0 hoac n=3
a) \(D=\frac{-21}{2}\) hoạc \(\frac{6n-21}{2-n}=\frac{18-21}{2-3}=3\)
b)\(D=\frac{-11-5\left(2-n\right)-n\left(2-n\right)}{2-n}=\frac{11}{n-2}-n-5\)
D nguyên=> n-2={-11,-1,1,11}=> n={-9,1.3.13}