Question

Consider the line \( L \) passing through the points \( (1, 2, 3) \) and \( (2, 3, 5) \). The distance of the point \[ \left( \frac{11}{3}, \frac{11}{3}, \frac{19}{3} \right) \] from the line \( L \) along the line \[ \frac{3x - 11}{2} = \frac{3y - 11}{1} = \frac{3z - 19}{2} \] is equal to:

• A. 3
• B. 5
• C. 4
• D. 6

Answer 1

The Correct Option is A

Step 1: Direction ratios of the given line

The direction ratios of the line:

\[ \frac{3x - 11}{2} = \frac{3y - 11}{1} = \frac{3z - 19}{2} \]

are:

\[ \vec{d} = \langle 2, 1, 2 \rangle \]

Step 2: Representing point \( B \)

Let point \( B \) on the given line be:

\[ B = (1 + \lambda, 2 + \lambda, 3 + 2\lambda), \]

where \(\lambda\) is the parameter.

Step 3: Direction ratios of line \( AB \)

Point \( A = \left(\frac{11}{3}, \frac{11}{3}, \frac{19}{3}\right) \). The direction ratios of \( AB \) are:

\[ \text{D.R. of } AB = \left\langle \frac{3\lambda - 8}{3}, \frac{3\lambda - 5}{3}, \frac{6\lambda - 10}{3} \right\rangle \]

Step 4: Parallel condition

Since \( AB \) lies along the direction vector \(\vec{d} = \langle 2, 1, 2 \rangle\), we have:

\[ \frac{\frac{3\lambda - 8}{3}}{2} = \frac{\frac{3\lambda - 5}{3}}{1} = \frac{\frac{6\lambda - 10}{3}}{2} \]

Simplify the first ratio:

\[ \frac{3\lambda - 8}{3 \cdot 2} = \frac{3\lambda - 5}{3} \]

Cross-multiply:

\[ 3\lambda - 8 = 6\lambda - 10 \]

Solve for \(\lambda\):

\[ 3\lambda = 2 \implies \lambda = \frac{2}{3} \]

Step 5: Find \( B \)

Substitute \(\lambda = \frac{2}{3}\) into \( B = (1 + \lambda, 2 + \lambda, 3 + 2\lambda) \):

\[ B = \left(1 + \frac{2}{3}, 2 + \frac{2}{3}, 3 + 2 \cdot \frac{2}{3}\right) = \left(\frac{5}{3}, \frac{8}{3}, \frac{13}{3}\right) \]

Step 6: Find distance \( AB \)

The distance \( AB \) is given by:

\[ AB = \sqrt{\left(\frac{11}{3} - \frac{5}{3}\right)^2 + \left(\frac{11}{3} - \frac{8}{3}\right)^2 + \left(\frac{19}{3} - \frac{13}{3}\right)^2} \]

Simplify each term:

\[ AB = \sqrt{\left(\frac{6}{3}\right)^2 + \left(\frac{3}{3}\right)^2 + \left(\frac{6}{3}\right)^2} \]

\[ AB = \sqrt{2^2 + 1^2 + 2^2} = \sqrt{4 + 1 + 4} = \sqrt{9} \]

Thus:

\[ AB = 3 \]

Final Answer:

\(Option (1) : \; 3\)