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If \(\begin{vmatrix}  1+2x & -1 \\ 6 & 3-x \end{vmatrix} = -3 \), find the...

Further Mathematics
WAEC 2015

If \(\begin{vmatrix}  1+2x & -1 \\ 6 & 3-x \end{vmatrix} = -3 \), find the values of x.

  • A. \(x = 3, -2\)
  • B. \(x = 4, \frac{-2}{3}\)
  • C. \(x = -4, \frac{3}{2}\)
  • D. \(x = 4, \frac{-3}{2}\)
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Correct Answer: Option D
Explanation

\(\begin{vmatrix} 1+2x & -1 \\ 6 & 3-x  \end{vmatrix} =  -3 \implies (1+2x)(3-x) - (-6) = -3\)

\(3 - x + 6x - 2x^{2} + 6 = -3\)

\(-2x^{2} + 5x + 3 + 6 + 3 = 0\)

Multiplying through with -1, 

\(2x^{2} - 5x -12 = 0\)

\((2x + 3)(x - 4) = 0 \implies x = \frac{-3}{2} , 4\)


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