The wavefront of a light beam is given by the equation x + 2y + 3x = c (where c is arbitrary constant), then the angle made by the direction of light with the y-axis is

The direction of light beam is perpendicular to the plane wavefront. ∴ direction of light is given by normal vector  n^ = i^ + 2j^+3j^12+22+32 =  i^ + 2j^+3j^14  Hence,  Angle made by the n^  with y-axis is given by  cosβ= n^ . j^  =( i^ + 2j^+3j^14) . (j^) =214