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If (x+2) and (x-1) are factors of 2kx2 + Lx + 24, find the values of L and k.

Mathematics

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Step-by-step solution

4 steps

To find the values of LL and kk, we use the Factor Theorem. The Factor Theorem states that if (x−a)(x-a) is a factor of a polynomial P(x)P(x), then P(a)=0P(a) = 0.

Let the given polynomial be P(x)=2kx2+Lx+24P(x) = 2kx^2 + Lx + 24.

  1. Use the factor (x+2)(x+2).

    If (x+2)(x+2) is a factor, then P(−2)=0P(-2) = 0.
    Substitute x=−2x = -2 into the polynomial:

    P(−2)=2k(−2)2+L(−2)+24=0P(-2) = 2k(-2)^2 + L(-2) + 24 = 0 2k(4)−2L+24=02k(4) - 2L + 24 = 0 8k−2L+24=08k - 2L + 24 = 0

    Divide the entire equation by 2:

    4k−L+12=04k - L + 12 = 0

    Rearrange to express LL in terms of kk:

    L=4k+12(∗)L = 4k + 12 \quad (*)
  2. Use the factor (x−1)(x-1).

    If (x−1)(x-1) is a factor, then P(1)=0P(1) = 0.
    Substitute x=1x = 1 into the polynomial:

    P(1)=2k(1)2+L(1)+24=0P(1) = 2k(1)^2 + L(1) + 24 = 0 2k+L+24=0(∗∗)2k + L + 24 = 0 \quad (**)
  3. Solve the system of linear equations.

    Substitute equation (∗)(*) into equation (∗∗)(**):

    2k+(4k+12)+24=02k + (4k + 12) + 24 = 0 6k+36=06k + 36 = 0 6k=−366k = -36 k=−366k = \frac{-36}{6} k=−6k = -6
  4. Substitute the value of kk back into equation (∗)(*) to find LL.

    L=4k+12L = 4k + 12 L=4(−6)+12L = 4(-6) + 12 L=−24+12L = -24 + 12 L=−12L = -12

    Thus, the values are L=−12L = -12 and k=−6k = -6.

    Comparing this with the given options:
    A. L = -12, k = -6
    B. L = -2, k = 1
    C. L = -2, k = -1
    D. L = 0, k = 1

    The calculated values match option A.

    The final answer is A. L = -12, k = -6\boxed{\text{A. L = -12, k = -6}}.

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