When the first two Chebyshev polynomials $T₀(x)$ and $T₁(x)$ are known, all other polynomials $T_{n}(x),n≥2$ can be obtained by means of the recurrence formula $$T_{n+1}(x)=2xT_{n}(x)-T_{n-1}(x)$$
My question is:
Does this formula holds true for $|x|>1$?
The recurrence generates new polynomials, and polynomials are always defined for all $x \in \Bbb R$.
So, yes, it also holds for $|x| > 1$.