Toán Lớp 8: thực hiện phép tính : (x+9/x^2-9) – (3 /x^2+3x)
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Toán Lớp 8: thực hiện phép tính : (x+9/x^2-9) – (3 /x^2+3x)
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\dfrac{{x + 9}}{{{x^2} – 9}} – \dfrac{3}{{{x^2} + 3x}}\\
= \dfrac{{x + 9}}{{\left( {x – 3} \right)\left( {x + 3} \right)}} – \dfrac{3}{{x\left( {x + 3} \right)}}\\
= \dfrac{{{x^2} + 9x}}{{x(x – 3)(x + 3)}} – \dfrac{{3x – 9}}{{x(x – 3)(x + 3)}}\\
= \dfrac{{{x^2} + 6x + 9}}{{x(x – 3)(x + 3)}} – \dfrac{{{{\left( {x + 3} \right)}^2}}}{{x(x – 3)(x + 3)}}\\
= \dfrac{{x + 3}}{{x\left( {x – 3} \right)}}
\end{array}\]