因为x²-1=﹙x-1﹚·﹙x+1﹚
原式=﹙x-3﹚/[﹙x-1﹚·﹙x+1﹚]-2·﹙x-1﹚/[﹙x-1﹚·﹙x+1﹚]
=[﹙x-3﹚-2·﹙x-1﹚]/[﹙x-1﹚·﹙x+1﹚]
=﹙x-3-2x+2﹚/[﹙x-1﹚·﹙x+1﹚]
=﹙-x-1﹚/[﹙x-1﹚·﹙x+1﹚]
=-﹙x+1﹚/[﹙x-1﹚·﹙x+1﹚]
=-1/﹙x-1﹚=1/﹙1-x﹚
因为x²-1=﹙x-1﹚·﹙x+1﹚
原式=﹙x-3﹚/[﹙x-1﹚·﹙x+1﹚]-2·﹙x-1﹚/[﹙x-1﹚·﹙x+1﹚]
=[﹙x-3﹚-2·﹙x-1﹚]/[﹙x-1﹚·﹙x+1﹚]
=﹙x-3-2x+2﹚/[﹙x-1﹚·﹙x+1﹚]
=﹙-x-1﹚/[﹙x-1﹚·﹙x+1﹚]
=-﹙x+1﹚/[﹙x-1﹚·﹙x+1﹚]
=-1/﹙x-1﹚=1/﹙1-x﹚