Geodesic
An extremal problem for algebraic polynomials with zero mean value on an interval
Matematičeskie zametki, Tome 62 (1997) no. 3, pp. 332-342 
V. V. Arestov; V. Yu. Raevskaya. An extremal problem for algebraic polynomials with zero mean value on an interval. Matematičeskie zametki, Tome 62 (1997) no. 3, pp. 332-342. http://geodesic.mathdoc.fr/item/MZM_1997_62_3_a1/
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     author = {V. V. Arestov and V. Yu. Raevskaya},
     title = {An extremal problem for algebraic polynomials with zero mean value on an interval},
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     pages = {332--342},
     year = {1997},
     volume = {62},
     number = {3},
     language = {ru},
     url = {http://geodesic.mathdoc.fr/item/MZM_1997_62_3_a1/}
}
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Voir la notice de l'article provenant de la source Math-Net.Ru

Let $\mathscr P_n^0(h)$ be the set of algebraic polynomials of degree $n$ with real coefficients and with zero mean value (with weight $h$) on the interval $[-1,1]$: $$ \int_{-1}^1h(x)p_n(x)dx=0; $$ here $h$ is a function which is summable, nonnegative, and nonzero on a set of positive measure on $[-1,1]$. We study the problem of the least possible value $$ i_n(h)=\inf\{\mu(p_n):p_n\in\mathscr P_n^0\} $$ of the measure $\mu(p_n)=\operatorname{mes}\{x\in[-1,1]:p_n(x)\ge0\}$ of the set of points of the interval at which the polynomial $p_n\in\mathscr P_n^0$ is nonnegative. We find the exact value of $i_n(h)$ under certain restrictions on the weight $h$. In particular, the Jacobi weight $$ h^{(\alpha,\beta)}(x)=(1-x)^\alpha(1+x)^\beta $$ satisfies these restrictions provided that $-1<\alpha,\beta\le0$.

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