题目内容：

2道高一数学证明题, 求计算过程 ,很简单的!
1. 证cosA+cos(120+B)+cos(120-B)/(sinB+sin(120+A)-sin(120-A)=tan(A+B)/2
R.H.S / L.H.S = .
=.
.
.
.
.
.= L.H.S. / R.H.S.
2. 证4cosθcos[(2π/3)+θ]cos[(2π/3)-θ] = cos3θ
R.H.S / L.H.S = .
=.
.
.
.
.
.= L.H.S. / R.H.S.

优质解答

1.[cosA+cos(120+B)+cos(120-B)]/[(sinB+sin(120+A)-sin(120-A)] cosA+cos120cosB-sin120sinB+cos120cosB+sin120sinB=------------------------------------------------------ sinB+sin120cosA+cos120sinA-sin120co...