Question

Difficulty: EasyFactoring Polynomials

Factor the trinomial x2+2x−15x^2 + 2x - 15. Which of the following choices shows the correct factorization?

  1. (x+5)(x−3)(x + 5)(x - 3)Answer
  2. B
    (x−5)(x+3)(x - 5)(x + 3)
  3. C
    (x+5)(x+3)(x + 5)(x + 3)
  4. D
    (x−15)(x+2)(x - 15)(x + 2)

Answer

The correct factorization is (x+5)(x−3)(x + 5)(x - 3).
To factor the quadratic expression x2+2x−15x^2 + 2x - 15, we need to find two numbers that multiply to −15-15 and add up to 22. The numbers 55 and −3-3 meet these criteria (5×−3=−155 \times -3 = -15 and 5+−3=25 + -3 = 2). Therefore, the completely factored form is (x+5)(x−3)(x + 5)(x - 3).

Step-by-Step Solution

1
Identify the target sum and product for the factors.
The target sum is the coefficient of the middle term (22), and the target product is the constant term (−15-15).
To factor a trinomial x2+bx+cx^2 + bx + c into (x+p)(x+q)(x + p)(x + q), we need to find two integers pp and qq that multiply to cc and add up to bb.
2
Find the two integers that satisfy both conditions.
The factor pairs of −15-15 are (−1,15)(-1, 15), (1,−15)(1, -15), (−3,5)(-3, 5), and (3,−5)(3, -5). The pair that adds to 22 is −3-3 and 55.
Checking the sums, only 5+(−3)=25 + (-3) = 2 provides the correct middle coefficient.
3
Write the factored form using the selected integers.
The factored form is (x+5)(x−3)(x + 5)(x - 3).
Substituting 55 and −3-3 into the binomial framework (x+p)(x+q)(x + p)(x + q) completes the factorization.

Key Concept

Factoring Monic Quadratic Trinomials
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