Question:

An equation of the plane passing through the line of intersection of the planes x + y + z = 6 and 2x + 3y + 4z + 5 = 0 and passing through (1, 1, 1) is

Updated On: Apr 30, 2026
  • 2x + 3y + 4z = 9
  • x + y + z = 3
  • x + 2y + 3z = 6
  • 20x + 23y + 26z = 69
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The Correct Option is D

Solution and Explanation

We are required to find the equation of a plane passing through the line of intersection of two planes and a point \((1,1,1)\).

Given planes:

\(P_1: x + y + z = 6\)

\(P_2: 2x + 3y + 4z + 5 = 0\)

Any plane passing through their line of intersection is written as:

\((x + y + z - 6) + \lambda(2x + 3y + 4z + 5) = 0\)

Expanding:

\((1 + 2\lambda)x + (1 + 3\lambda)y + (1 + 4\lambda)z + (5\lambda - 6) = 0\)

Since the plane passes through \((1,1,1)\), substitute these values:

\((1 + 2\lambda) + (1 + 3\lambda) + (1 + 4\lambda) + (5\lambda - 6) = 0\)

Simplify:

\(3 + 14\lambda - 6 = 0\)

\(14\lambda - 3 = 0\)

\(\lambda = \frac{3}{14}\)

Substitute back into the plane equation:

\((1 + 2\cdot \frac{3}{14})x + (1 + 3\cdot \frac{3}{14})y + (1 + 4\cdot \frac{3}{14})z + (5\cdot \frac{3}{14} - 6) = 0 \)

Simplifying coefficients:

\(\frac{20}{14}x + \frac{23}{14}y + \frac{26}{14}z - \frac{69}{14} = 0\)

Multiplying throughout by 14:

\(20x + 23y + 26z = 69\)

Final answer: \(20x + 23y + 26z = 69\)

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Concepts Used:

Equation of a Line in Space

In a plane, the equation of a line is given by the popular equation y = m x + C. Let's look at how the equation of a line is written in vector form and Cartesian form.

Vector Equation

Consider a line that passes through a given point, say ‘A’, and the line is parallel to a given vector '\(\vec{b}\)‘. Here, the line ’l' is given to pass through ‘A’, whose position vector is given by '\(\vec{a}\)‘.  Now, consider another arbitrary point ’P' on the given line, where the position vector of 'P' is given by '\(\vec{r}\)'.

\(\vec{AP}\)=𝜆\(\vec{b}\)

Also, we can write vector AP in the following manner:

\(\vec{AP}\)=\(\vec{OP}\)\(\vec{OA}\)

𝜆\(\vec{b}\) =\(\vec{r}\)\(\vec{a}\)

\(\vec{a}\)=\(\vec{a}\)+𝜆\(\vec{b}\)

\(\vec{b}\)=𝑏1\(\hat{i}\)+𝑏2\(\hat{j}\) +𝑏3\(\hat{k}\)