We know the distance of a point (x₀, y₀, z₀) from a plane Ax + By + Cz + D=0 …………… (1) is

On comparing, the equation of the given plane i.e.

2x - 3y + 6z + 21=0 with equation (1) we get,

A=2, B= - 3, C=6, D=21.

Again, we know that, the co - ordinates of the origin are

(0, 0, 0).

So, the length of the perpendicular drawn from the origin is

=3

Hence, the length of the perpendicular drawn from the origin to the plane 2x–3y + 6z + 21=0 is = 3 units.