Question

sina cos2a / cosa sin2a

Answer 1

$cfrac{sin alpha cos2 alpha }{cos alpha sin2 alpha } = cfrac{sin alpha (cos^2 alpha-sin^2 alpha ) }{cos alpha cdot 2sin alphacos alpha } = cfrac{cos^2 alpha-sin^2 alpha }{2cos ^2alpha } = \\ = cfrac{ cfrac{ cos^2 alpha}{cos ^2alpha}- cfrac{sin^2 alpha }{cos ^2alpha} }{ cfrac{2cos ^2alpha}{cos ^2alpha} } = cfrac{ 1-tg^2 alpha }{ 2 }$