`a)3x+12=0`
`=>3(x+4)=0`
`=>x+4=0`
`=>x=-4`
`b)x+2x=x-5`
`=>2x=-5`
`=>x=-5/2`
`c)2x(x-2)+5(x-2)=0`
`=>(2x+5)(x-2)=0`
`=>`\(\left[ \begin{array}{l}2x+5=0\\x-2=0\end{array} \right.\)
`=>`\(\left[ \begin{array}{l}x=-5/2\\x=2\end{array} \right.\)
`d)(3x-4)/2=(4x+1)/3`
`=>(3x-4).3=(4x+1).2`
`<=>9x-12=8x+2`
`<=>x=14`
`e)(2x)/(x-1)-x/(x+1)=1`
`<=>[(2x)(x+1)]/(x^2-1) -[x(x-1)]/(x^2-1)=[x^2-1]/[x^2-1]`
`=>2x^2+2x-x^2+x=x^2-1`
`<=>3x=-1`
`<=>x=-1/3`
`g)(x-3)/5+(1+2x)/3=6`
`<=>[(x-3).3]/15+[(1+2x).5]/15=90/15`
`=>3x-9+5+10x=90`
`<=>13x=-94`
`<=>x=-94/13`
`h)(2x-3)(x^2+1)=0`
`=>`\(\left[ \begin{array}{l}2x-3=0\\ x^{2}+1=0 \end{array} \right.\)
`=>`\(\left[ \begin{array}{l}x=3/2\\x^{2} =-1(vô lí)\end{array} \right.\)
`i)2/(x+1)-1/(x-2)=(3x-11)/[(x+1)(x-2)]`
`=>2(x-2)-(x+1)=3x-11`
`<=>2x-4-x-1=3x-11`
`<=>-2x=-6`
`<=>x=3`
