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Two line whose are (x-3)/(2)=(y-2)/(3)=(...

Two line whose are `(x-3)/(2)=(y-2)/(3)=(z-1)/(lambda) and (x-2)/(3)=(y-3)/(2)=(z-2)/(3)` lie in the same plane, then,
Q. Angle between the plane containing both the lines and the plane `4x+y+2z=0` is equal to

A

`(phi)/(3)`

B

`(phi)/(2)`

C

`(phi)/(6)`

D

`cos^(-1)((2)/(sqrt(186)))`

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The correct Answer is:
To solve the problem, we need to find the angle between the plane containing two given lines and the plane defined by the equation \(4x + y + 2z = 0\). ### Step-by-Step Solution: 1. **Identify the Lines**: The two lines are given as: \[ \frac{x-3}{2} = \frac{y-2}{3} = \frac{z-1}{\lambda} \quad \text{(Line 1)} \] \[ \frac{x-2}{3} = \frac{y-3}{2} = \frac{z-2}{3} \quad \text{(Line 2)} \] 2. **Extract Position and Direction Vectors**: - For Line 1, the position vector \( \mathbf{a_1} = (3, 2, 1) \) and the direction vector \( \mathbf{b_1} = (2, 3, \lambda) \). - For Line 2, the position vector \( \mathbf{a_2} = (2, 3, 2) \) and the direction vector \( \mathbf{b_2} = (3, 2, 3) \). 3. **Calculate \( \mathbf{a_2} - \mathbf{a_1} \)**: \[ \mathbf{a_2} - \mathbf{a_1} = (2-3, 3-2, 2-1) = (-1, 1, 1) \] 4. **Set Up the Scalar Triple Product**: The lines are coplanar if the scalar triple product \( (\mathbf{a_2} - \mathbf{a_1}) \cdot (\mathbf{b_1} \times \mathbf{b_2}) = 0 \). 5. **Calculate the Cross Product \( \mathbf{b_1} \times \mathbf{b_2} \)**: \[ \mathbf{b_1} = (2, 3, \lambda), \quad \mathbf{b_2} = (3, 2, 3) \] The cross product is calculated using the determinant: \[ \mathbf{b_1} \times \mathbf{b_2} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 2 & 3 & \lambda \\ 3 & 2 & 3 \end{vmatrix} \] Expanding this determinant: \[ = \mathbf{i}(3 \cdot 3 - 2 \cdot \lambda) - \mathbf{j}(2 \cdot 3 - 3 \cdot \lambda) + \mathbf{k}(2 \cdot 2 - 3 \cdot 3) \] \[ = \mathbf{i}(9 - 2\lambda) - \mathbf{j}(6 - 3\lambda) + \mathbf{k}(4 - 9) \] \[ = (9 - 2\lambda, -(6 - 3\lambda), -5) \] 6. **Set Up the Scalar Triple Product**: \[ (-1, 1, 1) \cdot (9 - 2\lambda, -(6 - 3\lambda), -5) = 0 \] This gives: \[ -1(9 - 2\lambda) + 1(-(6 - 3\lambda)) + 1(-5) = 0 \] Simplifying: \[ -9 + 2\lambda - 6 + 3\lambda - 5 = 0 \] \[ 5\lambda - 20 = 0 \implies \lambda = 4 \] 7. **Direction Vector of the Plane**: The direction vector of the plane containing the lines is \( \mathbf{c_1} = (9 - 2\lambda, -(6 - 3\lambda), -5) \) with \( \lambda = 4 \): \[ \mathbf{c_1} = (9 - 8, -6 + 12, -5) = (1, 6, -5) \] 8. **Normal Vector of the Given Plane**: The normal vector of the plane \( 4x + y + 2z = 0 \) is \( \mathbf{c_2} = (4, 1, 2) \). 9. **Calculate the Angle Between the Two Planes**: The cosine of the angle \( \theta \) between the two planes is given by: \[ \cos \theta = \frac{\mathbf{c_1} \cdot \mathbf{c_2}}{|\mathbf{c_1}| |\mathbf{c_2}|} \] First, calculate \( \mathbf{c_1} \cdot \mathbf{c_2} \): \[ \mathbf{c_1} \cdot \mathbf{c_2} = 1 \cdot 4 + 6 \cdot 1 - 5 \cdot 2 = 4 + 6 - 10 = 0 \] Since the dot product is zero, \( \cos \theta = 0 \) implies: \[ \theta = 90^\circ \] ### Final Answer: The angle between the plane containing both lines and the plane \( 4x + y + 2z = 0 \) is \( 90^\circ \).
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