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D( y )
y = 0
y^2 = 0
y = 0
y = 0
y^2 = 0
y^2 = 0
1*y^2 = 0 // : 1
y^2 = 0
y = 0
y in (-oo:0) U (0:+oo)
(5*y)/y-(10/y)-2-2 = 40/(y^2)-4 // - 40/(y^2)-4
(5*y)/y-(10/y)-(40/(y^2))-2-2+4 = 0
(5*y)/y-10*y^-1-40*y^-2-2-2+4 = 0
5-10*y^-1-40*y^-2 = 0
t_1 = y^-1
5-40*t_1^2-10*t_1^1 = 0
5-40*t_1^2-10*t_1 = 0
DELTA = (-10)^2-(-40*4*5)
DELTA = 900
DELTA > 0
t_1 = (900^(1/2)+10)/(-40*2) or t_1 = (10-900^(1/2))/(-40*2)
t_1 = -1/2 or t_1 = 1/4
t_1 = -1/2
y^-1+1/2 = 0
1*y^-1 = -1/2 // : 1
y^-1 = -1/2
-1 < 0
1/(y^1) = -1/2 // * y^1
1 = -1/2*y^1 // : -1/2
-2 = y^1
y = -2
t_1 = 1/4
y^-1-1/4 = 0
1*y^-1 = 1/4 // : 1
y^-1 = 1/4
-1 < 0
1/(y^1) = 1/4 // * y^1
1 = 1/4*y^1 // : 1/4
4 = y^1
y = 4
y in { -2, 4 }
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