It is (x-a1)n1 + (y-a2)n2 +(z-a3n3) = 0
Where (a1,a2 and a3) are coordinates of the point a, and n1,n2 and n3 are the direction ratios of vector n normal to the plane.
Therefore, you can remember that coefficients of x,y and z in the Cartesian equation of a plane are the direction ratios of normal to the plane.
Revision topic of
THREE DIMENSIONAL GEOMETRY