Đặt `A=({x+2}/{x+1}-{2x}/{x-1}). {3x+3}/x + {4x^2+x+7}/{x^2-x}` $(x\ne 0; x\ne ±1)$
`A={(x+2)(x-1)-2x(x+1)}/{(x+1)(x-1)} . {3(x+1)}/x + {4x^2+x+7}/{x(x-1)}`
`A={3(x^2-x+2x-2-2x^2-2x)}/{x(x-1)}+{4x^2+x+7}/{x(x-1)}`
`A={3(-x^2-x-2)+4x^2+x+7}/{x(x-1)}`
`A={-3x^2-3x-6+4x^2+x+7}/{x(x-1)}`
`A={x^2-2x+1}/{x(x-1)}={(x-1)^2}/{x(x-1)}`
`A={x-1}/x`
