ACT Math · Polynomial and rational functions

One solution to x³ - 2x² - 5x + 6 = 0 is x = 1. What is the sum of the other two solutions?

One solution to x3−2x2−5x+6=0x^3 - 2x^2 - 5x + 6 = 0 is x=1x = 1. What is the sum of the other two solutions?

Answer and explanation

Answer: F: 1

Since x=1x=1 is a root, divide by (x−1)(x-1) to get x2−x−6=(x−3)(x+2)x^2-x-6=(x-3)(x+2), so the other roots are 33 and −2-2. Their sum is 3+(−2)=13+(-2)=1, choice F. A faster check uses Vieta's formulas: the three roots sum to 22 (the opposite of the x2x^2 coefficient), and 2−1=12-1=1. Choice G, −1-1, reverses the sign of the sum. Choice H, 55, is the difference 3−(−2)3-(-2) rather than the sum. Choice J, −6-6, is the product of the two roots (and the constant term of the quotient), not their sum.

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