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Question
Evaluate the following determinant:
\[\begin{vmatrix}x & - 7 \\ x & 5x + 1\end{vmatrix}\]
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Solution
\[∆ = x(5x + 1) + 7x = 5 x^2 + x + 7x\]
\[ = 5 x^2 + 8x\]
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