JEE Mains · Maths · STD 12 - 3 and 4 . metrices and determinant
Among the statements:
I: If \( \begin{vmatrix} 1 & \cos \alpha & \cos \beta \\ \cos \alpha & 1 & \cos \gamma \\ \cos \beta & \cos \gamma & 1 \end{vmatrix} = \begin{vmatrix} 0 & \cos \alpha & \cos \beta \\ \cos \alpha & 0 & \cos \gamma \\ \cos \beta & \cos \gamma & 0 \end{vmatrix} \), then \( \cos^{2}\alpha+\cos^{2}\beta+\cos^{2}\gamma=\frac{3}{2} \)
II: If \( \begin{vmatrix} x^{2}+x & x+1 & x-2 \\ 2x^{2}+3x-1 & 3x & 3x-3 \\ x^{2}+2x+3 & 2x-1 & 2x-1 \end{vmatrix} = px+q \), then \( p^{2}=196q^{2} \),
- A both are false
- B only II is true
- C both are true
- D only I is true
Answer & Solution
Correct Answer
(A) both are false
Step-by-step Solution
Detailed explanation
Let \(\cos \alpha= x\) \(\cos \beta=y\) \(\cos \gamma= z\) \(\left|\begin{array}{lll}0 & x & y \\ x & 0 & z \\ y & z & 0\end{array}\right|=\left|\begin{array}{lll}1 & x & y \\ x & 1 & z \\ y & z & 1\end{array}\right|\) Expending both sides, we get \(x^2+y^2+z^2=1\) i.e.…
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