cos@sin(6п - @)(1 + ctg^2(-@)=ctg(-@)

cosα*sin(6π-α)*(1+ctg²(-α))=ctg(α)1. sin(6π-α)=-sinα2. 1+ctg²(-α)=1+ctg²α=1/sin²α3. cosα*(-sinα)/sin²α=-cosα/sinα=-ctgα4. ctg(-α)=-ctgα-ctgα=-ctgα