ACT Math · Polynomial and rational functions

Which expression is equivalent to (x²-4)/(x²+5x+6) for x ≠ -2, -3?

Which expression is equivalent to x2−4x2+5x+6\dfrac{x^2-4}{x^2+5x+6} for x≠−2,−3x \neq -2, -3?

Answer and explanation

Answer: F: x-2/x+3

Factor both parts: x2−4=(x−2)(x+2)x^2-4=(x-2)(x+2) and x2+5x+6=(x+2)(x+3)x^2+5x+6=(x+2)(x+3). Cancel the common factor x+2x+2, which is allowed since x≠−2x\ne-2: x−2x+3\frac{x-2}{x+3}, choice F. Check with x=0x=0: the original is −46=−23\frac{-4}{6}=-\frac{2}{3} and 0−20+3=−23\frac{0-2}{0+3}=-\frac{2}{3}. Choice G (x+2x+3\frac{x+2}{x+3}) cancels the wrong factor. Choice H (x−2x−3\frac{x-2}{x-3}) changes a sign in the denominator. Choice J (x−2x-2) cancels the entire denominator as if it were one factor. Only common factors, never common terms, can be cancelled. The restrictions x≠−2,−3x\ne-2,-3 stay in force after cancelling.

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