Question

How do you find the exact functional value Sin75° using the cosine sum or difference identity?

Answer 1

Write sin75 = sin(45+30) and then use the compound angle identity to rewrite it as sin45 cos30 + cos 45sin30.
The use the special triangles to evaluate this as (1/root2)(root2/2) + (1/root2)(1/2) = 1/2 + 1/2root2