1) 142-122=20 (куб.м) воды - израсходовано за сентябрь
7в-13в=-7-13
-6в=6
в=-1 не уверена
Решаем как квадрaтное ( arctgx = z)
D = 25- 16 = 9
arctgx = (5+3)/4 = 2 arctgx = (5-3)/4 = 1/2
-π/2 < arctg x < π/2, ⇒ arctg x = 1/2
X³-y³=(x-y)(x²+xy+y²)
x³-y³-5x(x²+xy+y²)
=(x-y)(x²+xy+y²)-5x(x²+xy+y²)=
=(x²+xy+y²)(x-y-5x)=
=(x²+xy+y²)(-y-4x)=
=-((x²+xy+y²)(4x+y)
4( x - 14) = x - 8
4x - 56 = x - 8
4x - x= -8 + 56
3x = 48
x = 16