Toán Lớp 8: bài 3:
A) x^2-4/9x^2-16
B) 2x-1/x^2-4x+4
C) 2/(X+1)(X-3)
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Toán Lớp 8: bài 3:
A) x^2-4/9x^2-16
B) 2x-1/x^2-4x+4
C) 2/(X+1)(X-3)
Comments ( 1 )
a)\frac{{{x^2} – 4}}{{9{x^2} – 16}}\left( {DKXD:9{x^2} – 16 \ne 0} \right)\\
\Leftrightarrow \frac{{\left( {x – 2} \right)\left( {x + 2} \right)}}{{\left( {3x – 4} \right)\left( {3x + 4} \right)}}\\
\Leftrightarrow \left[ \begin{array}{l}
3x – 4 \ne 0\\
3x + 4 \ne 0
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x \ne \frac{4}{3}\\
x \ne \frac{{ – 4}}{3}
\end{array} \right.\\
b)\frac{{2x – 1}}{{{x^2} – 4x + 4}}\left( {DKXD:{x^2} – 4x + 4 \ne 0} \right)\\
\Leftrightarrow {\left( {x – 2} \right)^2} \ne 0\\
\Leftrightarrow x – 2 \ne 0\\
\Leftrightarrow x \ne 2\\
c)\frac{2}{{\left( {x + 1} \right)\left( {x – 3} \right)}}\left( {DKXD:x + 1 \ne 0;x + 3 \ne 0} \right)\\
\Leftrightarrow \left[ \begin{array}{l}
x + 1 \ne 0\\
x + 3 \ne 0
\end{array} \right. \Leftrightarrow \left[ \begin{array}{l}
x \ne – 1\\
x \ne 3
\end{array} \right.
\end{array}\]