Or Let DR′ 's of normal is α,β and γ According to question, ‌‌‌α+2β+3γ=0. . . (i) ‌ and ‌‌‌−α+0β+γ=0 . . . (ii) ‌ On solving Eqs. (i) and (ii) by ‌ ‌ cross-multiplication, ‌ ‌‌‌‌‌‌
α
2−0
=‌
β
−3−1
=‌
γ
0+2
‌ So, ‌<α,β,γ>=<2,−4,2> ∴‌ DC's is ‌‌