The factors of the polynomial x3 - 6x2 + 11x - 6 are:

2018

The factors of the polynomial x3 - 6x2 + 11x - 6 are:

  1. A.

    (x + 1)(x + 2)(x - 3)

  2. B.

    (x - 1)(x + 2)(x - 3)

  3. C.

    (x - 1)(x - 2)(x - 3)

  4. D.

    (x - 1)(x - 2)(x + 3)

Attempted by 4 students.

Show answer & explanation

Correct answer: C

Concept

For a polynomial P(x), the Factor Theorem states that (x - r) is a factor exactly when P(r) = 0.

For a monic cubic with roots a, b and c, P(x) = (x - a)(x - b)(x - c). Its coefficients can be checked using the sum and products of the roots.

Application

  1. Evaluate P(1): 1 - 6 + 11 - 6 = 0. Therefore, (x - 1) is a factor.

  2. Divide P(x) by (x - 1). The quotient is x2 - 5x + 6.

  3. Find two numbers whose sum is 5 and product is 6. They are 2 and 3, so x2 - 5x + 6 = (x - 2)(x - 3).

  4. Hence, P(x) = (x - 1)(x - 2)(x - 3).

Cross-check

  1. First, (x - 2)(x - 3) = x2 - 5x + 6.

  2. Then, (x - 1)(x2 - 5x + 6) = x3 - 6x2 + 11x - 6, which reproduces the given polynomial.

Result: The factorization is (x - 1)(x - 2)(x - 3).

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