This is an implicit curve and a combination of the the curve of f(x) and its mirror images along the X and Y axis.
3
f(x) here is a sine approximation function I discovered
4
Expression 5: "f" left parenthesis, "x" , right parenthesis equals "x" StartRoot, 1 minus StartFraction, "x" squared Over 2 , EndFraction , EndRootfx=x1−x22
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Expression 6: "y" squared equals "f" left parenthesis, StartAbsoluteValue, "x" , EndAbsoluteValue , right parenthesis squaredy2=fx2