How to declare another variable for a polynomial [closed]

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n=var('n") def T(n): a=1 b=x if n==0: return a if n==1: return b else: for i in [2..n]: b=2xb-a a=(a+b)/(2*x) return b Could you help me to compute T(i) at x=1 or anything ?Mean that I want to declare x is a variable of T(i), but I can't. Thank you so much