12.设复数z1z_{1}z1,z2z_{2}z2在复平面内对应的点为Z1Z_{1}Z1,Z2Z_{2}Z2,若∣z1∣⩽2\vert z_{1}\vert \leqslant 2∣z1∣⩽2,z2=3−4iz_{2}=3-4iz2=3−4i,则∣Z1Z2→∣\vert \overrightarrow{{Z}_{1}{Z}_{2}}\vert∣Z1Z2∣的最大值为 [ 7 ].