(1 2/7у-1/2):2,5=5,2
9/7у-1/2=5,2*2,5
9/7у=13+1/2
9/7у=14,5
у=14,5:9/7
у=14,5*7/9
у=11,2778
2(x-y) * 3y^2
-------- ---------
y (x-y)(x+y)
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Сокращаем и умножаем
Получаем
6y^2
--------
x+y^2
1. =tg(21π/3 - π/3)=tg(7π - π/3)= -tg(π/3)= -√3
2. = -tg(31π/6) = - tg(30π/6 + π/6)= -tg(5π + π/6) =
= -tg(π/6)= - 1/√3 = -√3/3
3. =ctg(15π/3 + π/3)=ctg(5π + π/3) = ctg(π/3)= 1/√3 = √3/3