Energy stored in between the plates of parallel plate capacitor of...

Energy stored in capacitor of capacitance $C$ with voltage $V$ is, $U=\frac{1}{2} C V^2$ but $C=\frac{\varepsilon_0 A}{d}, V=E d$ where $A$ is the area of capacitor plate and $d$ is the distance of separation and $E$ is the electric field. \therefore \quad U=$\frac{1}{2} \frac{\varepsilon_0 A}{d}$E^2 d²=\frac{1}{2} \varepsilon_0 E² A d