Answer:
√2(√3 - 1)/4
Step-by-step explanation:
To find an exact value for Cos75°, we use the compound angle formula. Since 75° = 45° + 30°, Cos75° = Cos(45° + 30°).
Using Cos(A + B) = CosACosB - SinASinB where A = 45° and B = 30°,
Cos75° = Cos(45° + 30°) = Cos45°Cos30° - Sin45°Sin30°
Now Cos45° = Sin45° = 1/√2 = √2/2, Cos30° = √3/2 and Sin30° = 1/2.
Substituting these values into the above equation, we have
Cos75° = Cos(45° + 30°)
= Cos45°Cos30° - Sin45°Sin30°
= √2/2 × √3/2 - √2/2 × 1/2
= √6/4 -√2/4
= √2(√3 - 1)/4
