A slab of insulating material has thickness 2d and is oriented so that its faces are parallel to the yz-plane and given by the planes $x = d$ and $x = -d$. The $y$- and $z$-dimensions of the slab are very large compared to $d$; treat them as essentially infinite. The slab has a uniform positive charge density $\rho$. (a) Explain why the electric field due to the slab is zero at the center of the slab ($x =$ 0). (b) Using Gauss's law, find the electric field due to the slab (magnitude and direction) at all points in space.