Let \( f(x) = \begin{vmatrix} 3x^2 & \cos x & -\sin x \\ 6 & -1 & 0 \\ q & q^2 & q^3 \end{vmatrix} \) where \( q \) is any constant, then what is \( \frac{d^2}{dx^2}(f(x)) \) at \( x = 0 \) equal to ?
- A. -1
- B. 0 ✓
- C. 1
- D. q
Correct Answer: B. 0
Explanation
Differentiating the first row twice gives (6, -\cos x, \sin x). At x = 0, this row becomes (6, -1, 0), making the first two rows of the determinant identical. A determinant with two identical rows evaluates to 0.
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