MathematicsEquation of a PlaneJEE Advanced 2013Moderate
Visualized Solution (English)
Visualizing the Lines L1 and L2
- Given lines: L1:2x−1=−1y=1z+3
- Given lines: L2:1x−4=1y+3=2z+3
- Goal: Find the intersection point P of L1 and L2.
Defining General Points
- General point on L1: P1(2λ+1,−λ,λ−3)
- General point on L2: P2(μ+4,μ−3,2μ−3)
Equating the Coordinates
- Equating x and y coordinates:
- 1) 2λ+1=μ+4⇒2λ−μ=3
- 2) −λ=μ−3⇒λ+μ=3
Solving for λ and μ
- Adding (1) and (2): 3λ=6⇒λ=2
- Substituting λ=2 in (2): 2+μ=3⇒μ=1
- Check z: λ−3=2−3=−1 and 2μ−3=2(1)−3=−1.
- Consistency confirmed.
Finding the Intersection Point P
- Intersection point P at λ=2:
- x=2(2)+1=5
- y=−(2)=−2
- z=2−3=−1
- Point P=(5,−2,−1)
The Logic of the Normal Vector
- Required plane is perpendicular to P1:7x+y+2z=3 and P2:3x+5y−6z=4.
- Normal vectors: n1=(7,1,2) and n2=(3,5,−6).
- The required normal n is parallel to n1×n2.
Setting up the Cross Product
- Normal vector n=n1×n2=i^73j^15k^2−6
Calculating the Normal Vector
- Expanding the determinant:
- n=i^(−6−10)−j^(−42−6)+k^(35−3)
- n=−16i^+48j^+32k^
Simplifying Direction Ratios
- Direction ratios of the normal n:
- Dividing by −16: (1,−3,−2)
- So, a:b:c=1:−3:−2
The Equation of the Plane
- Equation of a plane: A(x−x1)+B(y−y1)+C(z−z1)=0
- Substitute point (5,−2,−1) and normal (1,−3,−2).
Substitution and Expansion
- Substituting values:
- 1(x−5)−3(y+2)−2(z+1)=0
- Expanding:
- x−5−3y−6−2z−2=0
The Final Plane Equation
- Simplifying the terms:
- x−3y−2z−13=0
- Standard form: x−3y−2z=13
- Comparing with ax+by+cz=d:
- a=1,b=−3,c=−2,d=13
Matching the Results
- Final Matching:
- a = 1 → (3)
- b = -3 → (2)
- c = -2 → (4)
- d = 13 → (1)
- Matching Sequence: P-3, Q-2, R-4, S-1
- Correct Option: (a)
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