4x/x+2 - 3x/x-2 - 12x/4-x²

Đáp án:

$\begin{array}{l}
\frac{{4x}}{{x + 2}} - \frac{{3x}}{{x - 2}} - \frac{{12x}}{{4 - {x^2}}}\left( {dkxd:x \ne  \pm 2} \right)\\
 = \frac{{4x}}{{x + 2}} - \frac{{3x}}{{x - 2}} - \frac{{12x}}{{\left( {2 - x} \right)\left( {2 + x} \right)}}\\
 = \frac{{4x\left( {x - 2} \right) - 3x\left( {x + 2} \right) + 12x}}{{\left( {x - 2} \right)\left( {2 + x} \right)}}\\
 = \frac{{4{x^2} - 8x - 3{x^2} - 6x + 12x}}{{\left( {x - 2} \right)\left( {2 + x} \right)}}\\
 = \frac{{{x^2} - 2x}}{{\left( {x - 2} \right)\left( {2 + x} \right)}}\\
 = \frac{{x\left( {x - 2} \right)}}{{\left( {x - 2} \right)\left( {2 + x} \right)}}\\
 = \frac{x}{{x + 2}}
\end{array}$