A Nonuniformly Charged Slab. A slab of insulating material has thickness $2 d$ and is oriented so that its faces are parallel to the $y z$ -plane and given by the planes $x=d$ and $x=-d$. The $y$ - and $z$ -dimensions of the slab are very large compared to $d$, so treat them as infinite. The slab has charge density given by $\rho(x)=\rho_{0}(x / d)^{2},$ where $\rho_{0}$ is a positive constant. Using Gauss's law, find the electric field due to the slab (magnitude and direction) at all points in space.