If 
is a trigonometric polynomial of degree 
satisfying the condition 
where 
is arbitrary and real, then 
.
Bernstein's Polynomial Theorem
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References
Szegö, G. Orthogonal Polynomials, 4th ed. Providence, RI: Amer. Math. Soc., p. 5, 1975.Referenced on Wolfram|Alpha
Bernstein's Polynomial TheoremCite this as:
Weisstein, Eric W. "Bernstein's Polynomial Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/BernsteinsPolynomialTheorem.html