`a)VT=(x^4+4)/(x(x²+2)-2x²-(x-1)²-1)`
`=(x^4+4+4x²-4x²)/(x^3+2x-2x^2-(x^2-2x+1)-1`
`=((x^4+4x^2+4)-4x^2)/((x^3-2x^2+2x)-(x^2-2x+1+1)`
`=((x^2+2)^2-(2x)^2)/(x(x^2-2x+2)-(x^2-2x+2)`
`=((x^2+2x+2)(x^2-2x+2))/((x^2-2x+2)(x-1)`
`=(x^2+2x+2)/(x-1)`
`=VP`
`⇒đpcm`