The equation of a plane passing through (x₁,y₁,z₁) and perpendicular to a line with direction ratios A, B, C is

A(x - x₁) + B(y - y₁) + C(z - z₁) = 0

The plane passes through P(1,2,3)

So, x₁ = 1, y₁ = 2, z₁ = - 3

Normal vector to plane =

where O(0,0,0), P(1,2, - 3)

Direction ratios of = (1 - 0), (2 - 0), (-3 - 0)

= (1,2, - 3)

∴ A = 1, B = 2, C = -3

Equation of plane in cartesian form is

1(x - 1) + 2(y - 2) - 3(z - (-3)) = 0

⇒ x - 1 + 2y - 4 - 3z - 9 = 0

⇒ x + 2y - 3z - 14 = 0