Theo Viet: \(\left\{{}\begin{matrix}x_1+x_2=\dfrac{3}{2}\\x_1x_2=-\dfrac{1}{2}\end{matrix}\right.\)
\(A=\dfrac{\left(x_1-1\right)\left(x_1+1\right)+\left(x_2-1\right)\left(x_2+1\right)}{\left(x_1+1\right)\left(x_2+1\right)}\)
\(=\dfrac{x_1^2+x_2^2-2}{x_1x_2+x_1+x_2+1}=\dfrac{\left(x_1+x_2\right)^2-2x_1x_2-2}{x_1x_2+x_1+x_2+1}\)
\(=\dfrac{\left(\dfrac{3}{2}\right)^2-2.\left(-\dfrac{1}{2}\right)-2}{-\dfrac{1}{2}+\dfrac{3}{2}+1}=...\)
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