JEE Challenger
More from Three Dimensional Geometry

Equation of Plane Passing Through Intersection of Two Planes

In R3\mathbb{R}^3, consider the planes P1:y=0P_1 : y = 0 and P2:x+z=1P_2 : x + z = 1. Let P3P_3 be a plane, distinct from P1P_1 and P2P_2, which passes through the line of intersection of P1P_1 and P2P_2. If the perpendicular distance of the point (0,1,0)(0, 1, 0) from P3P_3 is 11 and the distance of a point (α,β,γ)(\alpha, \beta, \gamma) from P3P_3 is 22, then which of the following relations is (are) true?

Options

A

2α+β+2γ+2=02\alpha + \beta + 2\gamma + 2 = 0

B

2α−β+2γ+4=02\alpha - \beta + 2\gamma + 4 = 0

Correct
C

2α+β−2γ−10=02\alpha + \beta - 2\gamma - 10 = 0

D

2α−β+2γ−8=02\alpha - \beta + 2\gamma - 8 = 0

Correct

Step-by-Step Solution

To find the equation of the plane P3P_3, we use the family of planes passing through the intersection of P1:y=0P_1 : y = 0 and P2:x+z−1=0P_2 : x + z - 1 = 0.

The general equation of such a plane P3P_3 (where P3P_3 is distinct from P1P_1) can be written as: (x+z−1)+λy=0(x + z - 1) + \lambda y = 0 Rearranging the terms, we get: x+λy+z−1=0x + \lambda y + z - 1 = 0

The perpendicular distance from the point (0,1,0)(0, 1, 0) to the plane P3P_3 is given to be 11: ∣0+λ(1)+0−1∣12+λ2+12=1\frac{|0 + \lambda(1) + 0 - 1|}{\sqrt{1^2 + \lambda^2 + 1^2}} = 1 ∣λ−1∣λ2+2=1\frac{|\lambda - 1|}{\sqrt{\lambda^2 + 2}} = 1

Squaring both sides: (λ−1)2=λ2+2(\lambda - 1)^2 = \lambda^2 + 2 λ2−2λ+1=λ2+2\lambda^2 - 2\lambda + 1 = \lambda^2 + 2 −2λ=1  ⟹  λ=−12-2\lambda = 1 \implies \lambda = -\frac{1}{2}

Substitute λ=−12\lambda = -\frac{1}{2} back into the equation of P3P_3: x−12y+z−1=0x - \frac{1}{2}y + z - 1 = 0 Multiplying the entire equation by 22, we obtain the equation of plane P3P_3: 2x−y+2z−2=02x - y + 2z - 2 = 0

Now, it is given that the perpendicular distance from the point (α,β,γ)(\alpha, \beta, \gamma) to P3P_3 is 22: ∣2α−β+2γ−2∣22+(−1)2+22=2\frac{|2\alpha - \beta + 2\gamma - 2|}{\sqrt{2^2 + (-1)^2 + 2^2}} = 2 ∣2α−β+2γ−2∣4+1+4=2\frac{|2\alpha - \beta + 2\gamma - 2|}{\sqrt{4 + 1 + 4}} = 2 ∣2α−β+2γ−2∣3=2\frac{|2\alpha - \beta + 2\gamma - 2|}{3} = 2 ∣2α−β+2γ−2∣=6|2\alpha - \beta + 2\gamma - 2| = 6

This leads to two possibilities:

  1. 2α−β+2γ−2=6  ⟹  2α−β+2γ−8=02\alpha - \beta + 2\gamma - 2 = 6 \implies 2\alpha - \beta + 2\gamma - 8 = 0
  2. 2α−β+2γ−2=−6  ⟹  2α−β+2γ+4=02\alpha - \beta + 2\gamma - 2 = -6 \implies 2\alpha - \beta + 2\gamma + 4 = 0

Thus, the relations that can be true are given by options (B) and (D).