Home Board Paper Solutions Text Book Solutions Articles NCERT Exemplar Solutions NCERT Books

# Class 12th Mathematics 2017 Set1 Delhi Board Paper Solution

Question 4

## If a line makes angles 90° and 60° respectively with the positive directions of x and y axes, find the angle which it makes with the positive direction of z-axis.

Here, α = 90° , β = 60°

Let γ = θº, where 0 ≤ θº ≤ π

Now cos2 α + cos2 β + cos2 γ = 1

⇒ cos2 90° + cos2 60° + cos2 θº = 1

⇒ 02 + (½)2 + cos2 θº = 1

cos2 θ = 1- 1/4 = 3/4

cos θ = ± √3 / 2

θ = π / 6  or  5π / 6