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x in (-oo:+oo)
(x*(x-3))/2 = 104 // - 104
(x*(x-3))/2-104 = 0
(x*(x-3))/2+(-104*2)/2 = 0
x*(x-3)-104*2 = 0
x^2-3*x-208 = 0
x^2-3*x-208 = 0
x^2-3*x-208 = 0
DELTA = (-3)^2-(-208*1*4)
DELTA = 841
DELTA > 0
x = (841^(1/2)+3)/(1*2) or x = (3-841^(1/2))/(1*2)
x = 16 or x = -13
(x+13)*(x-16) = 0
((x+13)*(x-16))/2 = 0
((x+13)*(x-16))/2 = 0 // * 2
(x+13)*(x-16) = 0
( x+13 )
x+13 = 0 // - 13
x = -13
( x-16 )
x-16 = 0 // + 16
x = 16
x in { -13, 16 }
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