JEE MAIN - Mathematics (2025 - 22nd January Evening Shift - No. 6)
Explanation
To find the perpendicular distance from the point $$P(2,-10,1)$$ to the line given by
$$\frac{x-1}{2}=\frac{y+2}{-1}=\frac{z+3}{2},$$
follow these steps:
Parametrize the Line:
From the given symmetric equations, set the common parameter as $$t$$:
$$x = 1 + 2t$$
$$y = -2 - t$$
$$z = -3 + 2t$$
This shows that:
A point on the line is $$A(1,-2,-3)$$ (when $$t=0$$).
The direction vector is $$\vec{d} = \langle 2, -1, 2 \rangle.$$
Determine the Vector from Point A to P:
Calculate
$$\vec{AP} = P - A = \langle 2 - 1, \; -10 - (-2), \; 1 - (-3) \rangle = \langle 1, \; -8, \; 4 \rangle.$$
Compute the Cross Product:
The formula for the perpendicular distance from a point to a line in 3D is:
$$d = \frac{\|\vec{AP} \times \vec{d}\|}{\|\vec{d}\|}.$$
First, find the cross product $$\vec{AP} \times \vec{d}$$:
$$ \vec{AP} \times \vec{d} = \begin{vmatrix} \mathbf{i} & \mathbf{j} & \mathbf{k} \\ 1 & -8 & 4 \\ 2 & -1 & 2 \end{vmatrix} = \Big( (-8)(2) - (4)(-1), \; (4)(2) - (1)(2), \; (1)(-1) - (-8)(2) \Big). $$
Evaluate each component:
First component: $$(-8 \times 2) - (4 \times -1) = -16 + 4 = -12.$$
Second component: $$ (4 \times 2) - (1 \times 2) = 8 - 2 = 6.$$
Third component: $$ (1 \times -1) - (-8 \times 2) = -1 + 16 = 15.$$
So,
$$\vec{AP} \times \vec{d} = \langle -12, 6, 15 \rangle.$$
Calculate the Magnitudes:
For the cross product:
$$ \|\vec{AP} \times \vec{d}\| = \sqrt{(-12)^2 + 6^2 + 15^2} = \sqrt{144 + 36 + 225} = \sqrt{405} = 9\sqrt{5}. $$
For the direction vector:
$$ \|\vec{d}\| = \sqrt{2^2 + (-1)^2 + 2^2} = \sqrt{4 + 1 + 4} = \sqrt{9} = 3. $$
Compute the Distance:
Substitute the magnitudes into the distance formula:
$$ d = \frac{9\sqrt{5}}{3} = 3\sqrt{5}. $$
Thus, the perpendicular distance from the point $$P(2,-10,1)$$ to the line is $$3\sqrt{5}$$.
Comparing with the options given, the correct answer is:
Option C: $$3\sqrt{5}$$.
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