polarization constant $k(n,x)=1$ for entire functions of exponential type

in this paper we will prove that if $l$ is a continuous symmetric n-linear form on a hilbert spaceand $widehat{l}$ is the associated continuous n-homogeneous polynomial, then $||l||=||widehat{l}||$.for the proof we are using a classical generalized  inequality due to s. bernstein for entire functions of exponential type. furthermore we study the case that if x is a banach space then we have that$$|l|=|widehat{l}|,;forall ;; l in{mathcal{l}}^{s}(^{n}x);.$$if the previous relation holds for every $l in {mathcal{l}}^{s}left(^{n}xright)$, then spaces${mathcal{p}}left(^{n}xright)$ and  $l in {mathcal{l}}^{s}(^{n}x)$ are isometric.we can also study the same problem using fr$acute{e}$chet derivative.