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JEE Main 2019
Matrices & Determinants
Matrices and Determinants
Medium

Question

Let θ(0,π2)\theta \in \left( {0,{\pi \over 2}} \right). If the system of linear equations (1+cos2θ)x+sin2θy+4sin3θz=0(1 + {\cos ^2}\theta )x + {\sin ^2}\theta y + 4\sin 3\,\theta z = 0 cos2θx+(1+sin2θ)y+4sin3θz=0{\cos ^2}\theta x + (1 + {\sin ^2}\theta )y + 4\sin 3\,\theta z = 0 cos2θx+sin2θy+(1+4sin3θ)z=0{\cos ^2}\theta x + {\sin ^2}\theta y + (1 + 4\sin 3\,\theta )z = 0 has a non-trivial solution, then the value of θ\theta is :

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Solution

This problem tests your understanding of homogeneous systems of linear equations and properties of determinants. For a system of homogeneous linear equations to have a non-trivial solution, the determinant of its coefficient matrix must be zero.

1. Key Concept: Non-Trivial Solutions for Homogeneous Systems

A system of linear equations of the form AX=0AX = 0 (where AA is the coefficient matrix, XX is the column vector of variables, and 00 is the zero vector) is called a homogeneous system.

  • It always has a trivial solution, X=0X=0 (i.e., x=0,y=0,z=0x=0, y=0, z=0).
  • For a homogeneous system to have a non-trivial solution (i.e.,

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