Докажите тождество sina-0.5sin2a*cosa/sin^2a=sina

(sin a - 0,5* 2* sin a* cosa * cos a) / sin^2 a = (sin a - sina * cos^2 a) / sin^2 a=
= sina( 1 - cos^2 a) / sin^2 a = sin a * sin^2 a / sin^2 a = sin a;
 sin a = sin a