MathematicsEquation of a PlaneJEE Advanced 2003Moderate
Visualized Solution (Hindi)
Visualizing the Problem
- Given points: A(2,1,0), B(5,0,1), and C(4,1,1)
- Objective: Find the equation of the plane passing through A,B, and C
The Determinant Formula
- The equation of a plane passing through (x1,y1,z1), (x2,y2,z2), and (x3,y3,z3) is:
- x−x1x2−x1x3−x1y−y1y2−y1y3−y1z−z1z2−z1z3−z1=0
Substituting the Coordinates
- Substituting A(2,1,0), B(5,0,1), and C(4,1,1):
- x−25−24−2y−10−11−1z−01−01−0=0
Simplifying the Determinant
- Simplifying the rows:
- x−232y−1−10z11=0
Expanding the Determinant
- Expanding along the first row:
- (x−2)(−1−0)−(y−1)(3−2)+z(0−(−2))=0
Final Plane Equation
- Simplifying the expression:
- −1(x−2)−1(y−1)+2z=0
- −x+2−y+1+2z=0
- Equation of the plane: x+y−2z=3
Introducing Point P and Image Q
- Given point P(2,1,6)
- Let Q(α,β,γ) be the image of P with respect to the plane x+y−2z=3
- Line PQ is perpendicular to the plane, and its midpoint M lies on the plane.
Direction of Line PQ
- Direction ratios of the normal to the plane: (1,1,−2)
- Equation of line PQ passing through P(2,1,6):
- 1x−2=1y−1=−2z−6=λ
General Coordinates of Q
- Coordinates of any point Q on the line:
- α=λ+2
- β=λ+1
- γ=−2λ+6
Finding the Midpoint M
- Midpoint M of PQ:
- M=(2(λ+2)+2,2(λ+1)+1,2(−2λ+6)+6)
- M=(2λ+4,2λ+2,212−2λ)
M Lies on the Plane
- Since M lies on x+y−2z=3:
- (2λ+4)+(2λ+2)−2(212−2λ)=3
Solving for Lambda
- Multiplying by 2:
- (λ+4)+(λ+2)−2(12−2λ)=6
- λ+4+λ+2−24+4λ=6
- 6λ−18=6⇒6λ=24⇒λ=4
Calculating Coordinates of Q
- Substituting λ=4 into Q(α,β,γ):
- α=4+2=6
- β=4+1=5
- γ=−2(4)+6=−2
- Point Q: (6,5,−2)
Summary and Conclusion
- Key Takeaways:
- Equation of plane: x+y−2z=3
- Image point Q: (6,5,−2)
- The line PQ is parallel to the normal vector n=i^+j^−2k^
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