1.(x^3-x^2-4x+1)/(x^2-3x+2)-(x^3-2x^2-9x+21)/(x^2-5x+6)+(x^2-3x+8)/(x^2-4x+3)
2.{(x^2)/(x-y)}*{y/(x+y)}-{(x^4y)/(x^4-y^4)}÷{(x^2/x^2+y^2)^2}
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