\(\dfrac{x-1}{x^3}-\dfrac{x+1}{x^3-x^2}+\dfrac{3}{x^3-2x^2+x}\) ( x # 0 ; x # 1)
\(=\dfrac{x-1}{x^3}-\dfrac{x+1}{x^2\left(x-1\right)}+\dfrac{3}{x\left(x^2-2x+1\right)}\)
\(=\dfrac{\left(x-1\right)^3}{x^3\left(x-1\right)^2}-\dfrac{x\left(x-1\right)\left(x+1\right)}{x^3\left(x-1\right)^2}+\dfrac{3x^2}{x^3\left(x-1\right)^2}\)
= x3 - 3x2 + 3x - 1 - x( x2 - 1) + 3x2
= x3 - 3x2 + 3x - 1 - x3 + x + 3x2
= 4x - 1
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