\(a+b+1=ab\)
\(\Leftrightarrow a+b+1-ab-2=-2\)
\(\Leftrightarrow b-1-ab+a=-2\)
\(\Leftrightarrow\left(b-1\right)-a\left(b-1\right)=-2\)
\(\Leftrightarrow\left(1-a\right)\left(b-1\right)=-2\)
\(\Rightarrow\left\{{}\begin{matrix}1-a=-1\\b-1=2\end{matrix}\right.\) hoặc \(\left\{{}\begin{matrix}1-a=1\\b-1=-2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}a=2\\b=3\end{matrix}\right.\) (a,b nguyên dương)
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