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Evaluating a limit by factoring and canceling

Consider the function f(x)=x3−3x2+2xx2−x.f(x) = \dfrac{x^3 - 3x^2 + 2x}{x^2 - x}.

Find lim⁡x→1x3−3x2+2xx2−x.\lim_{x \to 1} \frac{x^3 - 3x^2 + 2x}{x^2 - x}.

Hint

Direct substitution gives 0/00/0. Factor an xx out of both the numerator and denominator, then factor the remaining quadratic in the numerator to cancel the common factor causing the zero.

Step-by-step solution

Direct substitution at x=1x=1 gives 1−3+21−1=00\frac{1-3+2}{1-1} = \frac{0}{0}, an indeterminate form, so factoring is needed. Factor an xx from both numerator and denominator: numerator x3−3x2+2x=x(x2−3x+2)x^3-3x^2+2x = x(x^2-3x+2), and denominator x2−x=x(x−1)x^2-x = x(x-1). The quadratic factors further as x2−3x+2=(x−1)(x−2)x^2-3x+2=(x-1)(x-2), so f(x)=x(x−1)(x−2)x(x−1)f(x) = \dfrac{x(x-1)(x-2)}{x(x-1)}.

For x≠0,1x \neq 0,1, the common factors xx and (x−1)(x-1) cancel, leaving f(x)=x−2f(x) = x-2. Since limits depend only on behavior near x=1x=1 (not at x=1x=1 itself), we can substitute directly into the simplified expression: lim⁡x→1(x−2)=1−2=−1\lim_{x\to 1}(x-2) = 1-2 = -1.

Identifying the simplified linear expression

Hint
Step-by-step solution

After canceling the common factors of x and x minus one from numerator and denominator, the function simplified to x minus two. This simplified form was valid for all x except zero and one, and allowed direct substitution to evaluate the limit. The answer is x minus two.

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