Question:medium

A perpendicular is drawn from the point \( P(2,4,-1) \) to the line \( \frac{x+5}{1}=\frac{y+3}{4}=\frac{z-6}{-9} \). The equation of the perpendicular from \( P \) to the given line is

Show Hint

For perpendicular lines in 3D, use dot product = 0 condition.
Updated On: Jun 17, 2026
  • $\frac{x-2}{6}=\frac{y-4}{3}=\frac{z+1}{2}$
  • $\frac{x+2}{6}=\frac{y-4}{3}=\frac{z+1}{2}$
  • $\frac{x+2}{-6}=\frac{y-4}{3}=\frac{z+1}{2}$
  • $\frac{x+2}{6}=\frac{y+4}{3}=\frac{z+1}{2}$
Show Solution

The Correct Option is A

Solution and Explanation

To find the equation of the perpendicular from the point \( P(2,4,-1) \) to the given line, we need to understand the direction ratios of both the line and the perpendicular.

  1. The given line is represented as: \(\frac{x+5}{1} = \frac{y+3}{4} = \frac{z-6}{-9}\).
    • The direction ratios (dr) of the line are \( 1, 4, -9 \).
  2. The direction ratios of the perpendicular line, say \( a, b, c \), are such that the dot product with the direction ratios of the given line is zero, as they are perpendicular to each other. \(\Rightarrow a \cdot 1 + b \cdot 4 + c \cdot (-9) = 0\).
  3. Substitute the point \( P(2,4,-1) \) into the standard form of the line’s equation. A line with direction ratios \( a, b, c \) passing through the point \( (x_1,y_1,z_1) \) is represented as: \(\frac{x-x_1}{a} = \frac{y-y_1}{b} = \frac{z-z_1}{c}\).
    • Here, it is determined that:
      • \(x_1 = 2\)
      • \(y_1 = 4\)
      • \(z_1 = -1\)
  4. As the perpendicular line is expressed: \(\frac{x-2}{a} = \frac{y-4}{b} = \frac{z+1}{c}\).
  5. The question provides multiple choices for the direction ratios (which must satisfy the perpendicularity condition in (2)). By verification, the correct direction ratios are \( a = 6 \), \( b = 3 \), and \( c = 2 \), calculated using common sense or trial-error for the values:
    • Since \(
      a + 4b - 9c = 0\) must be true, a common solution is \( a = 6, b = 3, c = 2 \). Check that: \(6 \cdot 1 + 3 \cdot 4 + 2 \cdot (-9) = 0\), proving \( 6 + 12 - 18 = 0\), confirming perpendicularity.

Thus, the equation of the perpendicular line from \( P(2,4,-1) \) to the given line is:

 

$\frac{x-2}{6}=\frac{y-4}{3}=\frac{z+1}{2}$ 
 

 

The correct answer is therefore:

 

$\frac{x-2}{6}=\frac{y-4}{3}=\frac{z+1}{2}$ 
 

 

Was this answer helpful?
0