More alternatives for the steps:
Maybe this:
RegularPolygon[{1, Pi/4}, 8] //
CanonicalizePolygon //
Apply@Part //
Partition[#, 2, 1, 1] & //
Map[y == InterpolatingPolynomial[#, x] &]
Or this if have one with vertical and horizontal sides:
RegularPolygon[8] //
CanonicalizePolygon //
Apply@Part //
Partition[#, 2, 1, 1] & //
Map[
Quiet[Check[
y == InterpolatingPolynomial[#, x],
x == InterpolatingPolynomial[Reverse /@ #, y],
InterpolatingPolynomial::ipdup],
InterpolatingPolynomial::ipdup] &
](*//
ToRadicals//
FullSimplify*)