\(a,\dfrac{x^2-1}{x^2+2x+1}=\dfrac{\left(x-1\right)\left(x+1\right)}{\left(x+1\right)^2}\) (ĐK: \(x\ne-1\))
\(=\dfrac{x-1}{x+1}\)
Giá trị phân thức bằng 0 \(\Leftrightarrow x-1=0\Leftrightarrow x=1\)
\(b,\dfrac{x^2-5x+6}{x^2-4}=\dfrac{x^2-2x-3x+6}{\left(x-2\right)\left(x+2\right)}\) (ĐK: \(x\ne\pm2\))
\(=\dfrac{x\left(x-2\right)-3\left(x-2\right)}{\left(x-2\right)\left(x+2\right)}=\dfrac{\left(x-2\right)\left(x-3\right)}{\left(x-2\right)\left(x+2\right)}\)
\(=\dfrac{x-3}{x+2}\)
Giá trị phân thức bằng 0 \(\Leftrightarrow x-3=0\Leftrightarrow x=3\)
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