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JEE Main 2020
Matrices & Determinants
Matrices and Determinants
Medium

Question

Let α\alpha be a root of the equation x 2 + x + 1 = 0 and the matrix A = {1 \over {\sqrt 3 }}\left[ {\matrix{ 1 & 1 & 1 \cr 1 & \alpha & {{\alpha ^2}} \cr 1 & {{\alpha ^2}} & {{\alpha ^4}} \cr } } \right] then the matrix A 31 is equal to

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Solution

Key Concepts and Formulas

This problem primarily relies on the properties of the cube roots of unity and standard matrix multiplication.

  1. Cube Roots of Unity: The roots of the equation x31=0x^3 - 1 = 0 are 1,ω,ω21, \omega, \omega^2. The equation x2+x+1=0x^2+x+1=0 is derived from factoring x31=(x1)(x2+x+1)=0x^3-1=(x-1)(x^2+x+1)=0, so its roots are ω\omega and ω2\omega^2. Key properties include:
    • 1+ω+ω2=01 + \omega + \omega^2 = 0
    • ω3=1\omega^3 = 1
    • From ω3=1\omega^3=1, it

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