2 sin a/3 ctg a/3- cos a/3.Помогите решить))

[latex]2\sin\frac{\alpha}{3}\cot\frac{\alpha}{3}-\cos\frac{\alpha}{3}= 2\sin\frac{\alpha}{3}\frac{\cos\frac{\alpha}{3}}{\sin\frac{\alpha}{3}}-\cos\frac{\alpha}{3}=2\cos\frac{\alpha}{3}-\cos\frac{\alpha}{3}=\cos\frac{\alpha}{3}[/latex]