To compute the distance from the plane Ax + By + Cz + D = 0 to the point (0,0,0):
Compute A2 + B2 + C2.
Take the square root of the number from Step 1.
Compute the absolute value of D and divide it by the number from Step 2.
That's it! You can verify your result with an online distance from point to plane calculator.
Read more