Question

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Answer 1

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