The equation of the plane which passes through the z-axis and is perpendIcular to the line x−acosθ=y+2sinθ=z−30 is

The d.r’s of the normal of the plane are (cosθ,sinθ, 0).Now, the required plane passes through the z-axis.  hence the point (0,0,0) lies on the plane.The required plane is xcosθ+ysinθ=0, ⇒x+ytanθ=0