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Determinants, Adjoint & Inverse · Question 75 of 87

Question 75

MediumOriginal question

Read the two statements and choose the correct option.

I. If ∣A∣≠0|A| \ne 0, the system AX=BAX = B has a unique solution.

II. If ∣A∣=0|A| = 0 and (adj⁡A)B=O(\operatorname{adj} A)B = O, the system AX=BAX = B has no solution.

Options for question 75

Show the answer and explanation
CorrectNot quiteAnswer A

Correct answer: A

Explanation

  1. With ∣A∣≠0|A| \ne 0, A−1A^{-1} exists and X=A−1BX = A^{-1}B is the one solution, so I is true.

  2. With ∣A∣=0|A| = 0 and (adj⁡A)B=O(\operatorname{adj} A)B = O, the system may have infinitely many solutions (as 2x+3y=52x + 3y = 5, 4x+6y=104x + 6y = 10 does), so II is false.

Concept
Consistency tests
Typical time
90 s
Your time
—
The rule this testsConsistency of a system of equations
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Ten questions from Determinants, Adjoint & Inverse, at your own pace.

Practise this chapter →

Ten questions from Determinants, Adjoint & Inverse, at your own pace.