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x in (-oo:+oo)
x*((80-x)/3) = 5 // - 5
x*((80-x)/3)-5 = 0
(x*(80-x))/3-5 = 0
(x*(80-x))/3+(-5*3)/3 = 0
x*(80-x)-5*3 = 0
80*x-x^2-15 = 0
80*x-x^2-15 = 0
80*x-x^2-15 = 0
DELTA = 80^2-(-15*(-1)*4)
DELTA = 6340
DELTA > 0
x = (6340^(1/2)-80)/(-1*2) or x = (-6340^(1/2)-80)/(-1*2)
x = (2*1585^(1/2)-80)/(-2) or x = (-2*1585^(1/2)-80)/(-2)
(x-((2*1585^(1/2)-80)/(-2)))*(x-((-2*1585^(1/2)-80)/(-2))) = 0
((x-((2*1585^(1/2)-80)/(-2)))*(x-((-2*1585^(1/2)-80)/(-2))))/3 = 0
((x-((2*1585^(1/2)-80)/(-2)))*(x-((-2*1585^(1/2)-80)/(-2))))/3 = 0 // * 3
(x-((2*1585^(1/2)-80)/(-2)))*(x-((-2*1585^(1/2)-80)/(-2))) = 0
( x-((-2*1585^(1/2)-80)/(-2)) )
x-((-2*1585^(1/2)-80)/(-2)) = 0 // + (-2*1585^(1/2)-80)/(-2)
x = (-2*1585^(1/2)-80)/(-2)
( x-((2*1585^(1/2)-80)/(-2)) )
x-((2*1585^(1/2)-80)/(-2)) = 0 // + (2*1585^(1/2)-80)/(-2)
x = (2*1585^(1/2)-80)/(-2)
x in { (-2*1585^(1/2)-80)/(-2), (2*1585^(1/2)-80)/(-2) }
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