Verified answer

знаменатель: (cos84)^2 + (cos174)^2 = 1 - (sin84)^2 + (cos174)^2 =

1 + (cos174 - sin84)*(cos174 + sin84) = 1 + (cos(180-6) - sin(90-6))*(cos(180-6) + sin(90-6)) =

1 + (-cos(6) - cos(6))*(-cos6 + cos6) = 1

значит все выражение = 35