Question

найти cos2a если (cosa-2sina)/(sina-2cos)=-0.5

Answer 1

$frac{cosa-2sina}{sina-2cosa} =-0,5; ,; ; ; cos2a=?\\ frac{cosa-2sina}{sina-2cosa} =Big [frac{:cosa}{:cosa} Big ]= frac{1-2tga}{tga-2} =-0,5\\1-2tga=-0,5(tga-2)\\1-2tga=-0,5tga+1\\1,5tga=0; ; ; to ; ; ; tga=0\\Formyla:; ; ; cos2a= frac{1-tg^2a}{1+tg^2a} \\cos2a= frac{1-0}{1+0} =1$