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GATE 2020 BT – Question 56

Engineering Mathematics · Linear Algebra: Matrices and determinants, systems of linear equations, eigenvalues and eigenvectors · 2 marks · Numerical answer

The linear system $cx+y=5$, $3x+3y=6$ has no solution for which c?

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Correct answer: 1 to 1

Explanation

Divide the second equation by 3 to obtain x + y = 2. For inconsistent parallel lines, the left-hand sides must be proportional while the constants differ. This occurs at c = 1, when the first equation requires x + y = 5, contradicting x + y = 2. For c ≠ 1 the determinant is nonzero and there is a unique solution.

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