Question:medium

The distance of the point $(-3, 2, 3)$ from the line passing through $(4, 6, -2)$ and having direction ratios $-1, 2, 3$ is ________ units.

Show Hint

Use cross product formula for shortest distance.
Updated On: May 14, 2026
  • $2\sqrt{17}$
  • $4\sqrt{17}$
  • $2\sqrt{19}$
  • $4\sqrt{19}$
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Understanding the Concept:
We need to calculate the perpendicular distance from a given point $P$ to a line $L$ in 3D space. This can be efficiently computed using vector algebra by finding the magnitude of the cross product of the vector connecting a point on the line to $P$ and the line's direction vector. Step 2: Key Formula or Approach:
The perpendicular distance $d$ from a point $P$ to a line passing through point $A$ with direction vector $\bar{b}$ is: \[ d = \frac{|\vec{AP} \times \bar{b}|}{|\bar{b}|} \] where $\vec{AP}$ is the vector from point $A$ on the line to the given point $P$. Step 3: Detailed Explanation:
Let the given point be $P(-3, 2, 3)$.
The line passes through the point $A(4, 6, -2)$.
The direction vector of the line is $\bar{b} = -1\hat{i} + 2\hat{j} + 3\hat{k} = \langle -1, 2, 3 \rangle$.
First, construct the vector $\vec{AP}$: \[ \vec{AP} = \text{Position vector of } P - \text{Position vector of } A \] \[ \vec{AP} = \langle -3 - 4, 2 - 6, 3 - (-2) \rangle = \langle -7, -4, 5 \rangle \] \[ \vec{AP} = -7\hat{i} - 4\hat{j} + 5\hat{k} \] Next, compute the cross product $\vec{AP} \times \bar{b}$: \[ \vec{AP} \times \bar{b} = \begin{vmatrix} \hat{i} & \hat{j} & \hat{k}
-7 & -4 & 5
-1 & 2 & 3 \end{vmatrix} \] \[ = \hat{i}((-4)(3) - (5)(2)) - \hat{j}((-7)(3) - (5)(-1)) + \hat{k}((-7)(2) - (-4)(-1)) \] \[ = \hat{i}(-12 - 10) - \hat{j}(-21 + 5) + \hat{k}(-14 - 4) \] \[ = -22\hat{i} - \hat{j}(-16) - 18\hat{k} = \langle -22, 16, -18 \rangle \] Now, find the magnitude of this cross product vector: \[ |\vec{AP} \times \bar{b}| = \sqrt{(-22)^2 + 16^2 + (-18)^2} \] \[ |\vec{AP} \times \bar{b}| = \sqrt{484 + 256 + 324} = \sqrt{1064} \] Next, find the magnitude of the direction vector $\bar{b}$: \[ |\bar{b}| = \sqrt{(-1)^2 + 2^2 + 3^2} = \sqrt{1 + 4 + 9} = \sqrt{14} \] Finally, calculate the perpendicular distance $d$: \[ d = \frac{|\vec{AP} \times \bar{b}|}{|\bar{b}|} = \frac{\sqrt{1064}}{\sqrt{14}} = \sqrt{\frac{1064}{14}} \] \[ d = \sqrt{76} \] Simplify the radical: \[ d = \sqrt{4 \times 19} = 2\sqrt{19} \] Step 4: Final Answer:
The perpendicular distance is $2\sqrt{19}$ units.
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