Use appropriate sum or difference identities to find the exact value. cos 15°

Answer 1

cos(a-b) = cosacosb + sinasinb

use this fomula where a = 45 degrees and b = 30 degrees

so cos(45-30) = cos45cos30 + sin45sin30

since 45 and 30 are special angles, you can then find the exact values

Answer 2

cos 15°

cos (30° / 2)

√((1 + cos 30°) / 2)

√((1 + √3/2) / 2)

√((2 + √3) / 4)

√(2 + √3) / 2