Given, a line makes angles α, β and γ with positive directions of x-axis
Then l = cosα, m = cosβ and n = cosγ
Here sin2α + sin2β + sin2γ
= 1 – cos2α + 1 – cos2β + 1 – cos2γ
= 3 – (cos2α + cos2β + cos2γ)
= 3 – (l2 + m2 + n2)
= 3 – 1
i.e sin2α + sin2β + sin2γ = 2