A plane mirror is placed at the origin so that the direction ratios of its normal are (1, -1, 1). A ray of light, coming along the positive direction of the x-axis strikes the mirror. Then the direction ratios of the reflected ray are

Let (l, m, n) be the d.c’s of reflected ray We have (1, 0, 0) are the d.c’s of incident ray (x-axis).D.c’s of normal are 13,−13,13Let (l1,m1,n1)=(l,m,n),(l2,m2,n2)=(1,0,0)If θ is the angle between the normal to the plane and incident ray, then cosθ=13  l1+l22cosθ,m1+m22cosθ,n1+n22cosθ=(l,m,n)l+12cosθ=13⇒l=−13m−02cosθ=−13⇒m=−23  n+02cosθ=13⇒n=23