NCERT Solutions
Class 12 Maths
Three Dimensional Geometry

Ex.11.3 Q.3
Find the Cartesian equation of the following planes:
(a) r.(i + j + k) = 2
(b) r.(2i + 3j – 4k) = 1
(c) r.[(s – 2t)I + (3 - t)j + (2s + t)k] = 15
(a) It is given that equation of the plane is
r.(i + j + k) = 2 ………..1
For any arbitrary point P (x, y, z) on the plane, position vector r is given by,
r = xi + yj + zk
Substituting the value of r in equation 1, we obtain
(xi + yj + zk)(i + j − k) = 2
=> x + y − z = 2
This is the Cartesian equation of the plane.
(b) Given, r. (2i + 3j – 4k) = 1 .......1
For any arbitrary point P (x, y, z) on the plane, position vector r is given by,
r = xi + yj + zk
Substituting the value of r in equation 1, we obtain
(xi + yj + zk)(2i + 3j – 4k) = 1
=> 2x + 3y − 4z = 2
This is the Cartesian equation of the plane.
(c) r.[(s − 2t)I + (3 − t)j + (2s + t)k] = 15 .......1
For any arbitrary point P (x, y, z) on the plane, position vector r is given by,
r = xi + yj + zk
Substituting the value of r in equation 1, we obtain
(xi + yj + zk)[(s − 2t)i + (3 − t)j + (2s + t)k] = 15
=> (s − 2t)x + (3 − t)y + (2s + t)z = 15
This is the Cartesian equation of the plane.