sin2A=sinAcosA+sinAcosA=2sinAcosA=2×√3/4=√3/2
sin2A=√3/2=sinπ/3=sin2π/3
2A=π/3+2kπ 或 2A=2π/3+2kπ
解得
A=π/6+kπ 或 A=π/3+kπ k∈z