1. The value of the determinant with rows [1 2 3], [4 5 6] and [2 4 6] is
- A0
- B6
- C−6
- D12
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Answer: A. The third row is 2 times the first row. A determinant with two proportional rows is 0, so no expansion is needed.
By Team Megalecture · Updated 4 Nov 2026
14 exam-style questions on Maths · Matrices and determinants, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
14 questions · 1 topics · 10 per test
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
Answer: A. The third row is 2 times the first row. A determinant with two proportional rows is 0, so no expansion is needed.
Answer: B. The matrix is skew-symmetric of odd order 3, so its determinant is 0. Expanding confirms it: −a(0 − bc) − b(ac − 0) = abc − abc = 0.
Answer: A. A2 has rows [1 4] and [0 1], and A3 = A2A has rows [1 6] and [0 1]. Cubing each entry (giving 8) is not how matrix powers work.
Answer: B. Doubling the first equation gives 2x + 2y + 2z = 2, which contradicts 2x + 2y + 2z = 3. So there is no solution: the system is inconsistent.
Answer: D. A2 has rows [7 10] and [15 22]. Subtracting 5A (rows [5 10] and [15 20]) leaves rows [2 0] and [0 2], which is 2I.
Answer: A. Expand along the first row: 2(3 − 2) − (−1)(1 − 0) + 0 = 2 + 1 = 3. Forgetting the minus sign on the middle cofactor gives 2 − 1 = 1.
Answer: B. Transposing does not change a determinant, and multiplying a 2 × 2 matrix by 2 multiplies its determinant by 22 = 4. So |2At| = 4(−3) = −12.
Answer: B. The coefficient determinant k − 4 must be 0, so k = 4. Then doubling the first equation gives 2x + 4y = 6, which contradicts 2x + 4y = 5, so there is no solution.
Answer: A. The coefficient determinant 2(2) − 1(4) = 0, so there are non-trivial solutions: every pair with y = −2x works. A homogeneous system always has x = y = 0, so it is never inconsistent.
Answer: C. The inverse of a product reverses the order: (AB)(B−1A−1) = A(BB−1)A−1 = I. BtAt is (AB)t, the transpose, not the inverse.
14, each with the answer and a short explanation, across 1 topics: Matrices and determinants. Every chapter test draws ten of them, so you can take it many times.
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The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
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