\(B=\dfrac{9-3x+x^2-25-x^2+1}{\left(x+5\right)\left(x-1\right)}\cdot\dfrac{\left(x-1\right)\left(x+1\right)}{7\left(x-2\right)}=\dfrac{-3x-15}{\left(x+5\right)}\cdot\dfrac{\left(x+1\right)}{7\left(x-2\right)}\)
\(=\dfrac{-3x-3}{7\left(x-2\right)}\)
g: \(B=\dfrac{-3}{7}\cdot\dfrac{x+1}{x-2}\)
\(=\dfrac{-3}{7}\left(\dfrac{x-2+3}{x-2}\right)\)
\(=\dfrac{-3}{7}\left(x-2+\dfrac{3}{x-2}\right)>=-\dfrac{3}{7}2\sqrt{3}=\dfrac{-6\sqrt{3}}{7}\)
Dấu = xảy ra khi (x-2)^2=3
=>x=căn 3+2
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