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25*y^2 = (100-(4*x^2))/4 // - (100-(4*x^2))/4
25*y^2-((100-(4*x^2))/4) = 0
25*y^2-((100-4*x^2)/4) = 0
(-1*(100-4*x^2))/4+25*y^2 = 0
(-1*(100-4*x^2))/4+(4*25*y^2)/4 = 0
4*25*y^2-1*(100-4*x^2) = 0
4*x^2+100*y^2-100 = 0
(4*x^2+100*y^2-100)/4 = 0
(4*x^2+100*y^2-100)/4 = 0 // * 4
4*x^2+100*y^2-100 = 0
4*x^2 = -(100*y^2-100) // : 4
x^2 = (100-(100*y^2))/4
x^2 = (100-100*y^2)/4 // ^ 1/2
abs(x) = ((100-100*y^2)^(1/2))/2
x = ((100-100*y^2)^(1/2))/2 or x = -(((100-100*y^2)^(1/2))/2)
x in { ((100-100*y^2)^(1/2))/2, -(((100-100*y^2)^(1/2))/2) }
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