Math Problem Statement

If (2x - 1) is a factor of the polynomial P(x) = 2x^3 - 5x^2 - kx + 3, find the value of k. Find the other two factors of P(x).

Solution

The given problem states:

"If (2x1)(2x - 1) is a factor of the polynomial P(x)=2x35x2kx+3P(x) = 2x^3 - 5x^2 - kx + 3, find the value of kk. Find the other two factors of P(x)P(x)."

Step 1: Use the Factor Theorem

Since (2x1)(2x - 1) is a factor of the polynomial P(x)P(x), according to the factor theorem, the root of 2x1=02x - 1 = 0, which is x=12x = \frac{1}{2}, should satisfy P(12)=0P\left( \frac{1}{2} \right) = 0.

Let's substitute x=12x = \frac{1}{2} into the polynomial P(x)P(x):

P(x)=2x35x2kx+3P(x) = 2x^3 - 5x^2 - kx + 3

Substitute x=12x = \frac{1}{2}:

P(12)=2(12)35(12)2k(12)+3P\left( \frac{1}{2} \right) = 2\left( \frac{1}{2} \right)^3 - 5\left( \frac{1}{2} \right)^2 - k\left( \frac{1}{2} \right) + 3

Simplify each term:

P(12)=2(18)5(14)k2+3P\left( \frac{1}{2} \right) = 2\left( \frac{1}{8} \right) - 5\left( \frac{1}{4} \right) - \frac{k}{2} + 3 P(12)=2854k2+3P\left( \frac{1}{2} \right) = \frac{2}{8} - \frac{5}{4} - \frac{k}{2} + 3 P(12)=1454k2+3P\left( \frac{1}{2} \right) = \frac{1}{4} - \frac{5}{4} - \frac{k}{2} + 3

Now combine like terms:

P(12)=44k2+3P\left( \frac{1}{2} \right) = -\frac{4}{4} - \frac{k}{2} + 3 P(12)=1k2+3P\left( \frac{1}{2} \right) = -1 - \frac{k}{2} + 3 P(12)=2k2P\left( \frac{1}{2} \right) = 2 - \frac{k}{2}

Since P(12)=0P\left( \frac{1}{2} \right) = 0, we set the expression equal to zero:

2k2=02 - \frac{k}{2} = 0

Step 2: Solve for kk

2=k22 = \frac{k}{2} Multiply both sides by 2: k=4k = 4

Thus, the value of kk is 44.

Step 3: Find the other two factors

Now that we know k=4k = 4, the polynomial becomes:

P(x)=2x35x24x+3P(x) = 2x^3 - 5x^2 - 4x + 3

We are given that (2x1)(2x - 1) is one factor. To find the other factors, we can perform polynomial division of P(x)P(x) by 2x12x - 1.

Perform the division:

  1. Divide the leading term 2x32x^3 by 2x2x to get x2x^2.
  2. Multiply x2x^2 by 2x12x - 1, which gives 2x3x22x^3 - x^2.
  3. Subtract this from the original polynomial:

(2x35x24x+3)(2x3x2)=4x24x+3(2x^3 - 5x^2 - 4x + 3) - (2x^3 - x^2) = -4x^2 - 4x + 3

  1. Divide 4x2-4x^2 by 2x2x to get 2x-2x.
  2. Multiply 2x-2x by 2x12x - 1, which gives 4x2+2x-4x^2 + 2x.
  3. Subtract:

(4x24x+3)(4x2+2x)=6x+3(-4x^2 - 4x + 3) - (-4x^2 + 2x) = -6x + 3

  1. Divide 6x-6x by 2x2x to get 3-3.
  2. Multiply 3-3 by 2x12x - 1, which gives 6x+3-6x + 3.
  3. Subtract:

(6x+3)(6x+3)=0(-6x + 3) - (-6x + 3) = 0

Thus, the quotient from the division is x22x3x^2 - 2x - 3.

Step 4: Factor the quotient

Now we factor x22x3x^2 - 2x - 3. This factors as:

x22x3=(x3)(x+1)x^2 - 2x - 3 = (x - 3)(x + 1)

Final Answer:

The complete factorization of P(x)P(x) is:

P(x)=(2x1)(x3)(x+1)P(x) = (2x - 1)(x - 3)(x + 1)

Would you like further details or clarifications? Here are some related questions:

  1. How is the factor theorem applied to solve polynomial factorization problems?
  2. Can all cubic polynomials be factored into linear factors?
  3. How does polynomial division help in finding factors of higher-degree polynomials?
  4. What other methods can be used to factor polynomials besides division and the factor theorem?
  5. How can you check if your factorization of a polynomial is correct?

Tip: When factoring a cubic polynomial, always try the factor theorem first if you know one factor—it simplifies the process of finding the remaining factors.

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Math Problem Analysis

Mathematical Concepts

Algebra
Polynomials
Factorization
Polynomial Division

Formulas

Factor Theorem: If (ax - b) is a factor of P(x), then P(b/a) = 0
Polynomial division

Theorems

Factor Theorem
Polynomial Division

Suitable Grade Level

Grades 10-12