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x in (-oo:+oo)
y^2 = (15-(5*x^2))/3 // - (15-(5*x^2))/3
y^2-((15-(5*x^2))/3) = 0
y^2-((15-5*x^2)/3) = 0
(-1*(15-5*x^2))/3+y^2 = 0
(-1*(15-5*x^2))/3+(3*y^2)/3 = 0
3*y^2-1*(15-5*x^2) = 0
5*x^2+3*y^2-15 = 0
(5*x^2+3*y^2-15)/3 = 0
(5*x^2+3*y^2-15)/3 = 0 // * 3
5*x^2+3*y^2-15 = 0
5*x^2 = -(3*y^2-15) // : 5
x^2 = (15-(3*y^2))/5
x^2 = (15-3*y^2)/5 // ^ 1/2
abs(x) = ((15-3*y^2)^(1/2))/(5^(1/2))
x = ((15-3*y^2)^(1/2))/(5^(1/2)) or x = -(((15-3*y^2)^(1/2))/(5^(1/2)))
x in { ((15-3*y^2)^(1/2))/(5^(1/2)), -(((15-3*y^2)^(1/2))/(5^(1/2))) }
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