((sin5a-sina)/2cos3a)*ctg-1 упростить

[latex](\frac{sin5a-sina}{2cos3a})*ctga-1\\ sin5a-sina=2sin\frac{5a-a}{2}cos\frac{5a+a}{2}=2sin2acos3a;\\(\frac{2sin2acos3a}{2cos3a})*ctga-1=(sin2a)*ctga-1=\\(2sinacosa)*\frac{cosa}{sina}-1=2cos^2a-1=cos2a.[/latex] Формулы sin2a и cos2a: [latex]sin2a=2sinacos2a\\cos2a=cos^2a-sin^2a=cos^2a-(1-cos^2a)=2cos^2a-1[/latex]