Use d=∣nxx0+nyy0+nzz0−d∣nx2+ny2+nz2d = \frac{|n_x x_0 + n_y y_0 + n_z z_0 - d|}{\sqrt{n_x^2 + n_y^2 + n_z^2}}d=nx2+ny2+nz2∣nxx0+nyy0+nzz0−d∣.