Hello,
Sage relies on the user to be aware of precision problems, e.g.,

sage: ex=((x-1)^100).expand()
sage: ex.subs(x=1.1)
8.06715506374094e14
sage: ((x-1)^100).subs(x=1.1)
1.00000000000009e-100


or

sage: legendre_P(100,1.1)
1.35153125703123e18
sage: legendre_P(100,x).expand().subs(x=1.1)
1.46979621554052e23

would earn a shrug from developers because the user should know better
and substitute a value with higher precision.
In ticket #17066 the issue of polynomials is disguised. When implemented,
the user could encounter this:

sage: hypergeometric([1,-100],[3],0.7)
0.0278923450568346
sage: hypergeometric([1,-100],[3],x).subs(x=0.7)
-376.859920391941

Should the developer care (after having warned the user in the
documentation)? Please comment.

http://trac.sagemath.org/ticket/17066

Regards,

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