Theo hệ thức Viet: \(\left\{{}\begin{matrix}x_1+x_2=-7\\x_1x_2=-13\end{matrix}\right.\)
\(A=\left[\left(x_1-x_2\right)^2\right]^2+\sqrt{\left(x_1-x_2\right)^2}\)
\(=\left[\left(x_1+x_2\right)^2-4x_1x_2\right]^2+\sqrt{\left(x_1+x_2\right)^2-4x_1x_2}\)
\(=\left[\left(-7\right)^2-4.\left(-13\right)\right]^2+\sqrt{\left(-7\right)^2-4.\left(-13\right)}\)
\(=10201+\sqrt{101}\)