`a)` Với `x \ne +-1` có:
`VP=[x^2-x-2x+2]/[x^2-1]=[(x-1)(x-2)]/[(x-1)(x+1)]=[x-2]/[x+1]=VT`
`=>Đpcm`
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`b)` Với `x \ne 1/2` có:
`VT=[4x^3-x]/[5-10x]=[x(2x-1)(2x+1)]/[-5(2x-1)]=-[x(2x+1)]/5=-[2x^2+x]/5=VP`
`=>Đpcm`