упростите cos5/6 * cos/3 +sin5 /6sin /3 ------------------------------------------------------------ tg(3 /4- )
(cos5π/6cosπ/3+sin5π/6sinπ/3)/tg(3π/4-a)=cos(5π/6-π/3)/tg(3π/4-a) =cosπ/2:tg(3π/4-a)=0:tg(3π/4-a)=0