Multivariate Iyengar type inequalities for radial functions

Here we present a variety of multivariate Iyengar type inequalities for radial functions defined on the shell and ball. Our approach is based on the polar coordinates in $\mathbb{R}^{N}$, $N\geq 2$, and the related multivariate polar integration formula. Via this method we transfer well-known univariate Iyengar type inequalities and univariate author's related results into multivariate Iyengar inequalities.