This problem was given and I didn't give and point any ideas about it in the class in time. It says: if the group $G$ is perfect, then $Z\left(G/Z(G)\right)=\{1\}$, where $Z(G)$ is the centre of $G$. Can someone help me to tackle it well. Thank you!
Edit. A group $G$ is called perfect if $G=[G,G]$.