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JEE Main 2018
Matrices & Determinants
Matrices and Determinants
Medium

Question

If a1,a2,a3,.........,an,......{a_1},{a_2},{a_3},.........,{a_n},...... are in G.P., then the value of the determinant \left| {\matrix{ {\log {a_n}} & {\log {a_{n + 1}}} & {\log {a_{n + 2}}} \cr {\log {a_{n + 3}}} & {\log {a_{n + 4}}} & {\log {a_{n + 5}}} \cr {\log {a_{n + 6}}} & {\log {a_{n + 7}}} & {\log {a_{n + 8}}} \cr } } \right|, is

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Solution

Key Concepts

This problem combines the properties of Geometric Progressions (G.P.), logarithms, and determinants.

  1. Geometric Progression (G.P.): A sequence of numbers where each term after the first is found by multiplying the previous one by a fixed, non-zero number called the common ratio (rr). The kk-th term of a G.P. is given by ak=a1rk1a_k = a_1 r^{k-1}, where a1a_1 is the first term.
  2. Logarithm Properties:
    • log(XY)=logX+logY\log(XY) = \log X + \log Y
    • log(XY)=YlogX\log(X^Y) = Y \log X
  3. **Arithmetic Progression (A.

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