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x in (-oo:+oo)
k = t*((9*s-(5*t))/4) // - t*((9*s-(5*t))/4)
k-(t*((9*s-(5*t))/4)) = 0
k-(t*((9*s-5*t)/4)) = 0
(-1*t*(9*s-5*t))/4+k = 0
(-1*t*(9*s-5*t))/4+(4*k)/4 = 0
4*k-1*t*(9*s-5*t) = 0
4*k-9*s*t+5*t^2 = 0
(4*k-9*s*t+5*t^2)/4 = 0
(4*k-9*s*t+5*t^2)/4 = 0 // * 4
4*k-9*s*t+5*t^2 = 0
x belongs to the empty set
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