Question

sin15=coscos75=sin--,sin105=cos...最好有公式告我一下

Answer 1

sin15=cos75=sin(60-45)=sin(45-30)=cos(45+30)

sin(a + b) = sin(a)cos(b) + cos(α)sin(b)

cos(a + b) = cos(a)cos(b) - sin(a)sin(b)

sin(a - b) = sin(a)cos(b) - cos(a)sin(b)

cos(a - b) = cos(a)cos(b) + sin(a)sin(b)