Let E_n(ƒ) be the error of the best uniform approximation to a real function ƒ(x) on the interval [−1, 1] by real polynomials of no more than degree n. In the case of ƒ(x) = |x|, Bernstein^[2] showed that the limit

${\displaystyle \beta =\lim _{n\to \infty }2nE_{2n}(f),\,}$ 

called Bernstein's constant, exists and is between 0.278 and 0.286. His conjecture that the limit is:

${\displaystyle {\frac {1}{2{\sqrt {\pi }}}}=0.28209\dots \,.}$ 

was disproven by Varga and Carpenter,^[3] who calculated

${\displaystyle \beta =0.280169499023\dots \,.}$ 

• Weisstein, Eric W. "Bernstein's Constant". MathWorld.