High School

Calculate the product of the following determinants:

1. \begin{vmatrix} log_3 512 & log_4 3 \\ log_3 8 & log_4 9 \end{vmatrix}
2. \begin{vmatrix} log_2 3 & log_5 3 \\ log_3 4 & log_3 4 \end{vmatrix}

What is the result?

(a) 7
(b) 10
(c) 13
(d) 17

Answer :

To calculate the product of the two determinants, we first need to evaluate each determinant separately.

  1. Determinant 1:
    [tex]\begin{vmatrix} \log_3 512 & \log_4 3 \\ \log_3 8 & \log_4 9 \end{vmatrix}[/tex]

The determinant of a 2x2 matrix [tex]\begin{vmatrix} a & b \\ c & d \end{vmatrix}[/tex] is calculated as [tex]ad - bc[/tex].

Let's substitute in the values:

  • [tex]a = \log_3 512[/tex]
  • [tex]b = \log_4 3[/tex]
  • [tex]c = \log_3 8[/tex]
  • [tex]d = \log_4 9[/tex]

The determinant becomes:
[tex]\log_3 512 \cdot \log_4 9 - \log_4 3 \cdot \log_3 8[/tex]

We can simplify terms using logarithmic identities:

  • [tex]\log_3 512 = \log_3 (2^9) = 9 \cdot \log_3 2[/tex]
  • [tex]\log_4 9 = \log_4 (3^2) = 2 \cdot \log_4 3[/tex]
  • [tex]\log_3 8 = \log_3 (2^3) = 3 \cdot \log_3 2[/tex]
  • [tex]\log_4 3[/tex] remains as it is.

Thus, the determinant is:
[tex](9 \cdot \log_3 2)(2 \cdot \log_4 3) - (\log_4 3)(3 \cdot \log_3 2)[/tex]

Simplifying this gives us:
[tex]18(\log_3 2)(\log_4 3) - 3(\log_3 2)(\log_4 3)[/tex]
[tex]= 15(\log_3 2)(\log_4 3)[/tex]

  1. Determinant 2:
    [tex]\begin{vmatrix} \log_2 3 & \log_5 3 \\ \log_3 4 & \log_3 4 \end{vmatrix}[/tex]

We notice that the second column values are identical, meaning the determinant is zero because any column that is repeated in this arrangement results in a determinant of zero. Let's see this step:
[tex]\log_2 3 \cdot \log_3 4 - \log_5 3 \cdot \log_3 4[/tex]
[tex]= \log_3 4(\log_2 3 - \log_5 3)[/tex]

Since the terms become zero:
[tex]\log_3 4 \cdot (\log_2 3 - \log_5 3) = 0[/tex]

Thus, the determinant is 0.

Therefore, the product of the two determinants is:
[tex]15(\log_3 2)(\log_4 3) \cdot 0 = 0[/tex]

The correct option is not listed. If you have additional information, such as a correction to the terms or a typographical error, let me know!