截面问题

题1: 5．已知直四棱柱$ABCD-A_{1}B_{1}C_{1}D_{1}$，底面$ABCD$是菱形，$\angle ADC=\frac{2\pi }{3}$，且$A

题2: 3．已知正方体$ABCD-A_{1}B_{1}C_{1}D_{1}$中，$AB=2\sqrt{3}$，点$E$为平面$A_{1}BD$内的动点，设直线$AE$与