你好森燃!
这掘春逗判卖里用到以下公式:
cos2a = 2cos²a - 1 ===> cos²a = (1+cos2a) /2
cos(a-b)=cosacosb+sinasinb
asinx + bcosx = √(a²+b²) sin(x +φ) ,tanφ = b/a
cos²B + cos²(2π/3 - B)
= (1+cos2B)/2 + [1+ cos(4π/3 - 2B) ] /2
= 1/2 + 1/2 cos2B + [ 1 - 1/2 cos2B - √3 /2 sin2B ] / 2
= 1 + 1/4 cos2B - √3 /4 sin2B
= 1 + 1/2 sin(2B - π/6)
这我不怎么清楚了