\(a+b=a.b\)
\(\Leftrightarrow a-ab+b=0\)
\(\Leftrightarrow a-b\left(a-1\right)=0\)
\(\Leftrightarrow a-1-b\left(a-1\right)=-1\)
\(\Leftrightarrow\left(a-1\right)\left(1-b\right)=-1\)
\(\Leftrightarrow\left(a-1\right)\left(1-b\right)=-1.1=1.\left(-1\right)\)
\(\Leftrightarrow\left[\begin{matrix}a-1=1\Rightarrow1-b=-1\Rightarrow a=2;b=2\\a-1=-1\Rightarrow1-b=1\Rightarrow a=0;b=0\end{matrix}\right.\)
\(\Leftrightarrow\left(a;b\right)=\left\{\left(2;2\right),\left(0;0\right)\right\}\)
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