Rational Functions Math Example 4

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Example 4

hard
Find all asymptotes (vertical, horizontal, and oblique) of f(x)=x2+2x3x1f(x) = \frac{x^2 + 2x - 3}{x - 1}. Does the function have a hole or a vertical asymptote at x=1x = 1?

Solution

  1. 1
    Factor the numerator: x2+2x3=(x+3)(x1)x^2 + 2x - 3 = (x + 3)(x - 1). So f(x)=(x+3)(x1)x1f(x) = \frac{(x+3)(x-1)}{x-1}.
  2. 2
    The (x1)(x-1) cancels: f(x)=x+3f(x) = x + 3 for x1x \neq 1. Since the factor cancels, x=1x = 1 is a hole (not a vertical asymptote). Hole at (1,4)(1, 4).
  3. 3
    No vertical asymptotes remain. The simplified form x+3x + 3 is linear, so there is an oblique asymptote y=x+3y = x + 3 (which the function equals everywhere except the hole). No horizontal asymptote.

Answer

Hole at (1,4). Oblique asymptote: y=x+3. No vertical or horizontal asymptotes.\text{Hole at } (1, 4). \text{ Oblique asymptote: } y = x + 3. \text{ No vertical or horizontal asymptotes.}
When a factor cancels between numerator and denominator, it creates a hole (removable discontinuity), not a vertical asymptote. The degree of the numerator exceeding the denominator by 1 indicates an oblique asymptote found by polynomial division.

About Rational Functions

A rational function is a ratio of two polynomials: f(x)=P(x)/Q(x)f(x) = P(x)/Q(x) where PP and QQ are polynomials and Q(x)0Q(x) \neq 0.

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