Question

Докажите тождество:
sinαсоsα-tg/1-(sinα+сosα)^2=1/2tg^2α

Answer 1

Объяснение:

$\frac{sin\alpha cos\alpha -tg\alpha }{1-(sin+cos)^2} =\frac{sin\alpha *cos\alpha -\frac{sin\alpha }{cos\alpha } }{1-(sin^2\alpha +2*sin\alpha *cos\alpha +cos^2\alpha } =\frac{\frac{sin\alpha *cos^2\alpha -sin\alpha }{cos\alpha } }{1-(1+2*sin\alpha *cos\alpha )} =\frac{\frac{sin\alpha *cos^2\alpha -sin\alpha }{cos\alpha } }{1-1-2*sin\alpha *cos\alpha } =$$=\frac{sin\alpha *(cos^2\alpha -1)}{cos\alpha *(-2*sin\alpha *cos\alpha )}=\frac{sin\alpha *(-sin^2\alpha )}{-2*sin\alpha *cos^2\alpha } =\frac{-sin^3\alpha }{-2*sin\alpha *cos^2\alpha }=\frac{sin^2\alpha }{2*cos^2\alpha } =\frac{1}{2}tg^2\alpha .$