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Determinants, Adjoint & Inverse · Question 6 of 87

Question 6

EasyOriginal question

If ∣x342∣=6\begin{vmatrix} x & 3 \\ 4 & 2 \end{vmatrix} = 6, what is xx?

Options for question 6

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. The determinant is 2x−122x - 12.

  2. 2x−12=62x - 12 = 6 gives 2x=182x = 18, so x=9x = 9.

Worth noting

−3-3 comes from 2x+12=62x + 12 = 6: the product 12 was added instead of subtracted.

Concept
An unknown in a determinant
Typical time
60 s
Your time
—
The rule this testsThe determinant of a matrix
Practise this chapter →

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

Practise this chapter →

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