BITSAT 2012 Paper

Using cosine formula
2 sin (θ + Φ) cos (θ – Φ) = 1/2 .....(i)
2 cos (θ + Φ) cos (θ – Φ) =3/2 .....(ii)
Squaring (1) and (2) and then adding
4cos2 (ϕ - Φ) =

1

4

+

9

4

=

5

2

⇒ cos2 (θ – Φ) =

5

8