JAMB 2010 Mathematics · Question 34

If $\begin{vmatrix} x & 3 \\ 2 & 7 \end{vmatrix} = 15$ , find the value of x

Options

Answer: A. 3

Explanation written with AI and checked against the answer key

Analyze the question: We are given a 2×2 determinant that equals 15, and we need to find x. Concept: For a 2×2 determinant, | a b | | c d | = ad − bc Solution: Here a = x, b = 3, c = 2, d = 7. Determinant = (x)(7) − (3)(2) = 7x − 6 Set it equal to 15: 7x − 6 = 15 7x = 21 x = 3 Check: 7(3) − 6 = 21 − 6 = 15 ✓ Answer: x = 3, which is option A. Tip: Remember "main diagonal minus the other diagonal" (ad − bc). Always substitute your answer back in to confirm. It takes only a few seconds and protects you from sign errors.

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If ∣x327∣=15\begin{vmatrix} x & 3 \\ 2 & 7 \end{vmatrix} = 15​x2​37​​=15, find the value of x

Options

Answer: A. 3

If $\begin{vmatrix} x & 3 \\ 2 & 7 \end{vmatrix} = 15$ , find the value of x