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The value of ∣log⁡51022log⁡105∣\left|\begin{array}{cc}\log_5 10 & 2 \\[4pt] 2 & \log_{10} 5\end{array}\right| is

Solution

✅ Correct Option: 1

For a 2×22 \times 2 matrix ∣abcd∣\begin{vmatrix} a & b \\ c & d \end{vmatrix}, the determinant =ad−bc= ad - bc

So our determinant:

=(log⁡510)(log⁡105)−(2)(2)= (\log_5 10)(\log_{10} 5) - (2)(2)

=(log⁡510)(log⁡105)−4= (\log_5 10)(\log_{10} 5) - 4


Using the change of base identity:

log⁡ab×log⁡ba=1\log_a b \times \log_b a = 1

This is because log⁡ab=1log⁡ba\log_a b = \dfrac{1}{\log_b a}, so multiplying them gives 11.

Here, a=5a = 5 and b=10b = 10:

log⁡510×log⁡105=1\log_5 10 \times \log_{10} 5 = 1


Substituting back:

=1−4= 1 - 4

=−3= -3

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