Question

Difficulty: MediumFactoring Polynomials

Which of the following expressions is equivalent to 6x2−15x−366x^2 - 15x - 36 and is factored completely?

  1. 3(2x+3)(x−4)3(2x + 3)(x - 4)Answer
  2. B
    (2x+3)(3x−12)(2x + 3)(3x - 12)
  3. C
    3(2x−3)(x+4)3(2x - 3)(x + 4)
  4. D
    3(2x+1)(x−12)3(2x + 1)(x - 12)

Answer

The completely factored expression is 3(2x+3)(x−4)3(2x + 3)(x - 4).
The correct answer identifies the GCF of 3 and correctly factors the remaining quadratic 2x2−5x−122x^2 - 5x - 12 into (2x+3)(x−4)(2x + 3)(x - 4). Expanding this result confirms it equals 6x2−15x−366x^2 - 15x - 36 and no further factors can be extracted.

Step-by-Step Solution

1
Identify and factor out the greatest common factor (GCF) from all three terms.
3(2x2−5x−12)3(2x^2 - 5x - 12)
The coefficients 6, -15, and -36 are all divisible by 3.
2
Find two numbers that multiply to acac (where a=2a=2 and c=−12c=-12, so 2×−12=−242 \times -12 = -24) and add to the middle coefficient (b=−5b=-5).
The numbers are −8-8 and 33.
(−8)×3=−24(-8) \times 3 = -24 and (−8)+3=−5(-8) + 3 = -5.
3
Rewrite the trinomial by splitting the middle term using these two numbers.
3(2x2−8x+3x−12)3(2x^2 - 8x + 3x - 12)
This sets up the polynomial for factoring by grouping.
4
Factor the trinomial by grouping.
3[2x(x−4)+3(x−4)]=3(2x+3)(x−4)3[2x(x - 4) + 3(x - 4)] = 3(2x + 3)(x - 4)
Factoring out (x−4)(x - 4) from both groups provides the final completely factored form.

Key Concept

Factoring out a GCF followed by factoring a non-monic trinomial.
Rate this question