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## Main Question or Discussion Point

For a plane with equation Ax + By + Cz + D = 0, the normal vector is (A, B, C).

However, this plane equation can also be rewritten as (-A)x + (-B)y + (-C)z + (-D) = 0, in which case the normal vector is (-A, -B, -C) which is in the opposite direction as the other normal vector.

Basically my question is this - what's the direction of a normal vector - i.e. both directions seem correct.

However, this plane equation can also be rewritten as (-A)x + (-B)y + (-C)z + (-D) = 0, in which case the normal vector is (-A, -B, -C) which is in the opposite direction as the other normal vector.

Basically my question is this - what's the direction of a normal vector - i.e. both directions seem correct.