Respuesta :

sqdancefan
The formula for the distance from a point (x, y, z) to the plane ax +by +cz +d = 0 is this:
.. distance = |ax +by +cz +d|/√(a^2 +b^2 +c^2)

For your point and plane, that is
.. distance = |-8 -2*7 -4*6 -8|/√(1^2 +2^2 +4^2)
.. = 54/√21
.. = (18/7)√21