(x^2+1)(x-2)-x^3=-2x^2
x^3-2x^2+x-2-x^3=-2x^2
-2x^2+x-2=-2x^2
x-2=0
x-2
tg9-tg63+tg81-tg27 =
= tg9+tg81-(tg27+tg63) =
= tg9+tg(90-9) - (tg27+tg(90-27)) =
= tg9+Ctg9 - (tg27+Ctg) =
= 1/(cos9*sin9)-1/(cos27*sin27) =
= 2/sin18 - 2/sin54 =
= 2*(sin54-sin18)/(sin18*cos36) =
= 2*2*sin18*cos36/(sin18*cos36) = 4
Запишем все ввиде обыкновенных дробей
21/100:3/8+11/25=
Перевернем вторую дробь
21/100*8/3+11/25=
Сокращаем
7/25*2/1+11/25=14/25+11/25=25/25=1