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x in (-oo:+oo)
y = x*(900-((3*x)/4)) // - x*(900-((3*x)/4))
y-(x*(900-((3*x)/4))) = 0
y-(x*((-3/4)*x+900)) = 0
y-1*x*(900-3/4*x) = 0
y-1*x*(900-3/4*x) = 0
3/4*x^2-900*x+y = 0
3/4*x^2-900*x+y = 0
3/4*x^2-900*x+y = 0
DELTA = (-900)^2-(3/4*4*y)
DELTA = 810000-3*y
810000-3*y = 0
810000-3*y = 0 // - 810000
-3*y = -810000 // : -3
y = -810000/(-3)
y = 270000
DELTA = 0 <=> t_3 = 270000
x = 900/(3/4*2) i y = 270000
x = 600 i y = 270000
( x = ((810000-3*y)^(1/2)+900)/(3/4*2) or x = (900-(810000-3*y)^(1/2))/(3/4*2) ) i y > 270000
( x = 2/3*((810000-3*y)^(1/2)+900) or x = 2/3*(900-(810000-3*y)^(1/2)) ) i y > 270000
y-270000 > 0
y-270000 > 0 // + 270000
y > 270000
x in { 600, 2/3*((810000-3*y)^(1/2)+900), 2/3*(900-(810000-3*y)^(1/2)) }
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