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Exercise 7.2 · Q13

Q.Find the value of ∣1log⁡xylog⁡xzlog⁡yx1log⁡yzlog⁡zxlog⁡zy1∣\begin{vmatrix} 1 & \log_x y & \log_x z \\ \log_y x & 1 & \log_y z \\ \log_z x & \log_z y & 1 \end{vmatrix} if x,y,z≠1x, y, z \neq 1.

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Change-of-base turns the entries into ratios of logarithms; row scaling makes all three rows identical, giving determinant 00.

Use the change-of-base rule log⁡xy=ln⁡yln⁡x\log_x y = \dfrac{\ln y}{\ln x}. Let p=ln⁡xp = \ln x, q=ln⁡yq = \ln y, r=ln⁡zr = \ln z (all nonzero since x,y,z≠1x,y,z\neq1).

Step 1. The determinant becomes

∣1q/pr/pp/q1r/qp/rq/r1∣.\begin{vmatrix} 1 & q/p & r/p \\ p/q & 1 & r/q \\ p/r & q/r & 1 \end{vmatrix}.

Step 2. Multiply R1R_1 by pp, R2R_2 by qq, R3R_3 by rr; this multiplies the determinant by pqrpqr:

pqr⋅D=∣pqrpqrpqr∣.pqr\cdot D = \begin{vmatrix} p & q & r \\ p & q & r \\ p & q & r \end{vmatrix}. …

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