Solutions
Given:
Equation of plane P1 : x + 2y + 3z - 2 = 0
Equation of plane P2 : x - y + z - 3 = 0
The plane through the intersection of above planes is at a distance
from the point (3, 1, -1)
Concept:
Equation of plane passing through the intersection of two planes P1 and P2 can be assumed as :
P1 + λP2 = 0
Formula:
The distance of a point (p, q, r) from a plane ax + by + cz = d is given by :

Calculation:
Using P1 + λP2 = 0,
Equation of plane through the intersection of above planes is -
(x + 2y + 3z - 2) + λ(x - y + z - 3) = 0 ---- (i)
⇒ (1 + λ)x + (2 - λ)y + (3 + λ)z + (-2 - 3λ) = 0

On solving, λ = -7/2
Putting λ = -7/2 in equation (i), we get equation of plane as -
-5x + 11y - z + 17 = 0
⇒ 5x - 11y + z - 17 = 0
∴ a + b + c - 17 = - 22