如图，在$\mathit{\Delta ABC}$中，已知$\mathit{AC}=3$，$\mathit{BC}=4$，点$D$为边$\mathit{AB}$的中点，连结$\mathit{CD}$，过点$A$作$\mathit{AE}\perp \mathit{CD}$于点$E$，将$\mathit{\Delta ACE}$沿直线$\mathit{AC}$翻折到$\mathit{\Delta ACE}\text{'}$的位置．若$\mathit{CE}\text{'}//\mathit{AB}$，则$\mathit{CE}\text{'}=$　　．