1. proximately twenty years ago children wore strictly school uniform at school. but since the 1990s school uniform has been cancelled. children chose themselves a school dress. anyway, many schools nowadays have school uniform. is it good or had? this question has both advantages and disadvantages.now, let`s consider positive aspects.firstly, the school uniform has strictness which make children study at school more seriously.further more, school uniform makes children more disciplined.more than that it isn`t very expensive. and every family can afford to buy it.more over, school uniform removes social inequality because both rich and poor children wear the same clothes.further more, there is no such a question what to put on in the morning. now, let`s pay our attention, to same negative aspects.school uniform prevents children to be individuality. all are a like. one more, every day one and the same clothes.by the end of the school year it becomes untidy and not pleasant to look at. all in all school uniform has advantages and disadvantages, but as for me personally i vote for the school uniform because i presume it convenient for pupils.извини второе не могу у меня мозг не компьютер
1) по теореме косинусов имеем: a² = b² + c² - 2bc cos a = 25 - 24 cos 135° = 25 + 12√2 a = √(25 + 12√2) по теореме синусов, a / sin a = b / sin b sin b = sin a · b / a = √2 / 2 · 3 / √(25 + 12√2) = 3 / √(50 + 24√2) ∠b = arcsin(3 / √(50 + 24√2)) ∠c = 180° - 135° - ∠b = 45° - arcsin(3 / √(50 + 24√2)) 2) ∠a = 180° - ∠b - ∠c = 65° по теореме синусов b / sin b = a / sin a b = a sin b / sin a = 24.6 · √2 / 2 / (sin 65°) = 123√2 / (10 sin 65°) по теореме синусов c / sin c = a / sin a c = a sin c / sin a = 24.6 ·sin 70° / sin 65°
3·sin²x - 2·cosx + 2=0
Так как sin²x=1-cos²x, то
3·(1-cos²x) - 2·cosx + 2=0
3 - 3·cos²x-2·cosx+2=0 | ·(-1)
3·cos²x+2·cosx-5=0
Введём обозначение: cosx=t . Так как |cosx|≤1, то |t|≤1.
Получим квадратное уравнение:
3·t² + 2·t - 5=0
D= 2²-4·3·(-5) = 4+60 = 64 = 8²
t₁= (-2-8)/(2·3) = -10/6= -5/3 < -1 - не подходит
t₂= (-2+8)/(2·3) = 6/6 = 1
Сделаем обратную замену для t₂= 1:
cosx= 1, отсюда получаем
ответ: x=2·π·n, n∈Z.