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x in (-oo:+oo)
3*x*((x+20)/2) = 85 // - 85
3*x*((x+20)/2)-85 = 0
(3*x*(x+20))/2-85 = 0
(3*x*(x+20))/2+(-85*2)/2 = 0
3*x*(x+20)-85*2 = 0
3*x^2+60*x-170 = 0
3*x^2+60*x-170 = 0
3*x^2+60*x-170 = 0
DELTA = 60^2-(-170*3*4)
DELTA = 5640
DELTA > 0
x = (5640^(1/2)-60)/(2*3) or x = (-5640^(1/2)-60)/(2*3)
x = (2*1410^(1/2)-60)/6 or x = (-2*1410^(1/2)-60)/6
(x-((-2*1410^(1/2)-60)/6))*(x-((2*1410^(1/2)-60)/6)) = 0
((x-((-2*1410^(1/2)-60)/6))*(x-((2*1410^(1/2)-60)/6)))/2 = 0
((x-((-2*1410^(1/2)-60)/6))*(x-((2*1410^(1/2)-60)/6)))/2 = 0 // * 2
(x-((-2*1410^(1/2)-60)/6))*(x-((2*1410^(1/2)-60)/6)) = 0
( x-((-2*1410^(1/2)-60)/6) )
x-((-2*1410^(1/2)-60)/6) = 0 // + (-2*1410^(1/2)-60)/6
x = (-2*1410^(1/2)-60)/6
( x-((2*1410^(1/2)-60)/6) )
x-((2*1410^(1/2)-60)/6) = 0 // + (2*1410^(1/2)-60)/6
x = (2*1410^(1/2)-60)/6
x in { (-2*1410^(1/2)-60)/6, (2*1410^(1/2)-60)/6 }
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