Question

cos(45 ∘ +θ).cos(45 ∘ −θ)= 2 1 ​ cos 2 θ

Answer 1

Answer:

Correct option is A)

cosθ=178⇒sinθ=1715

Now,

cos(30+θ)+cos(45−θ)+cos(120−θ)=cos(30+θ)+cos(45−θ)+cos(60+θ)=cos30cosθ−sin30sinθ+cos45cosθ+sin45sinθ+cos60cosθ−sin60sinθ=23.178−21.1715+21.178+21.1715+21.178−23