Find the exact value of the cosine of 75 degrees.
Since we can write 75 degrees as the sum of 45 and 30 degrees, we can write
cos(75°) = cos(45° + 30°) = cos45°cos30° - sin45°sin30° ... Can someone explain how to get 45 and 30

Question

Find the exact value of the cosine of 75 degrees.
Since we can write 75 degrees as the sum of 45 and 30 degrees, we can write
cos(75°) = cos(45° + 30°) = cos45°cos30° - sin45°sin30° ... Can someone explain how to get 45 and 30

anonymous · Answer

because 45 + 30 = 75 ?

anonymous · Answer

You need to use the rules of special triangles 30-30-60 and 45-45-90.
Do you know those?