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D( x )
x = 0
x = 0
x = 0
x in (-oo:0) U (0:+oo)
y*((x+20)/5) = (2*y)/x // - (2*y)/x
y*((x+20)/5)-((2*y)/x) = 0
y*((x+20)/5)-2*x^-1*y = 0
(y*(x+20))/5+(-2*y)/x = 0
(x*y*(x+20))/(5*x)+(-2*5*y)/(5*x) = 0
x*y*(x+20)-2*5*y = 0
x^2*y+20*x*y-10*y = 0
x^2*y+20*x*y-10*y = 0
y*(x^2+20*x-10) = 0
x^2+20*x-10 = 0
DELTA = 20^2-(-10*1*4)
DELTA = 440
DELTA > 0
x = (440^(1/2)-20)/(1*2) or x = (-440^(1/2)-20)/(1*2)
x = (2*110^(1/2)-20)/2 or x = (-2*110^(1/2)-20)/2
y*(x-((-2*110^(1/2)-20)/2))*(x-((2*110^(1/2)-20)/2)) = 0
(y*(x-((-2*110^(1/2)-20)/2))*(x-((2*110^(1/2)-20)/2)))/(5*x) = 0
(y*(x-((-2*110^(1/2)-20)/2))*(x-((2*110^(1/2)-20)/2)))/(5*x) = 0 // * 5*x
y*(x-((-2*110^(1/2)-20)/2))*(x-((2*110^(1/2)-20)/2)) = 0
( x-((-2*110^(1/2)-20)/2) )
x-((-2*110^(1/2)-20)/2) = 0 // + (-2*110^(1/2)-20)/2
x = (-2*110^(1/2)-20)/2
( x-((2*110^(1/2)-20)/2) )
x-((2*110^(1/2)-20)/2) = 0 // + (2*110^(1/2)-20)/2
x = (2*110^(1/2)-20)/2
x in { (-2*110^(1/2)-20)/2, (2*110^(1/2)-20)/2 }
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