Prove that: cos105∘+cos15∘=sin75∘−sin15∘
LHS: sin75∘−sin15∘ =cos(90∘+15∘)+cos(90∘−15∘) =−sin(15∘+sin75∘ =sin75∘−sin15∘ ∴cos105∘+cos15∘=sin75∘−sin15∘ Hence proved.
Evaluate ∣∣∣cos15sin15sin75cos75∣∣∣