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200-(9*(1/3)*x^2) = 0
200-3*x^2 = 0
-3*x^2 = -200 // : -3
x^2 = 200/3
x^2 = 200/3 // ^ 1/2
abs(x) = (200/3)^(1/2)
x = (200/3)^(1/2) or x = -(200/3)^(1/2)
x in { (200/3)^(1/2), -(200/3)^(1/2) }
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