Line is passing through point P(4,+2,7) and direction ratios (1,1,2) and lies on the given plane ax+by+z=7 So, point will satisfy the equation of plane a(4)+b(+2)+(7)=7 4a+2b=0 .....(i) Now direction ratios of the line and direction ratios of the plane will be perpendicular so their product must be zero