Question

Sinα×cosα(tgα-ctg(-α))

Answer 1

$sina*cosa(tga-(-ctga))=sina*cosa*(tga+ctga)=\\\\=sina*cosa*( \frac{sina}{cosa} + \frac{cosa}{sina})=sina*cosa* \frac{sin^2a+cos^2a}{sina*cosa}=\\\\=sina*cosa* \frac{1}{sina*cosa}=1$