`b,[x+4]/[x-4]-3/x=12/[x(x-4)]``ĐKXĐ:x≠0;x≠4`
`⇔[x(x+4)-3(x-4)]/[x(x-4)]=12/[x(x-4)]`
`⇒x^2+4x-3x+12=12`
`⇔x^2+x=12-12`
`⇔x(x+1)=0`
`⇔`\(\left[ \begin{array}{l}x=0\\x+1=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=0(loại)\\x=-1(t/m)\end{array} \right.\)
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`c,[x+3]/[x-3]-21/[x(x-3)]=7/x` `ĐKXĐ:x≠0;x≠3`
`⇔[x(x+3)-21]/[x(x-3)]=[7(x-3)]/[x(x-3)]`
`⇒x^2+3x-21=7x-21`
`⇔x^2+3x-7x=-21+21`
`⇔x^2-4x=0`
`⇔x(x-4)=0`
`⇔`\(\left[ \begin{array}{l}x=0\\x-4=0\end{array} \right.\)
`⇔`\(\left[ \begin{array}{l}x=0(loại)\\x=4(t/m)\end{array} \right.\)
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`g,2/[x+1]-1/[x-2]=[3x-11]/[(x+1)(x-2)]``ĐKXĐ:x≠-1;x≠2`
`⇔[2(x-2)-1(x+1)]/[(x+1)(x-2)]=[3x-11]/[(x+1)(x-2)]`
`⇒2x-4-x-1=3x-11`
`⇔2x-x+3x=-11+1+4`
`⇔4x=-6`
`⇔x=-6/4`
`⇔x=-3/2`
Vậy...
