The fourth question (1) should be connected by Q*N*, so the CD is parallel and equal to 1/2q * n *. Q*N* parallelism equals AB, so CD parallelism equals 1/2AB, so quadrilateral ABCD is trapezoidal. (2) MP is connected to AB in O, M*P* in H is connected to CD, Q*N* is connected to O*, and O * is connected to OH. So OO* is perpendicular to the plane M*N*P*Q*. Because CD belongs to the plane M*N*P*Q*, OO* is perpendicular to CD. And because CD is perpendicular to M*P* and the intersection point is O*, CD is perpendicular to the plane MPP*M*. Because OH belongs to plane MPP*M*, OH is the height of trapezoidal ABCD. So CD is equal to two thirds of the root number 2a, AB is equal to the root number 2a, and OH is equal to three quarters of the root number 2a ... So according to the area formula of trapezoid, it can be concluded that the area of trapezoid ABCD is equal to the square of nine eighths × a.

The fifth question is to connect EE 1, FF 1. Then find out that the quadrilateral EFF 1E 1 is a parallelogram (very simple, I don't need to say this). So EF is parallel to E 1F 1, and ef = E 1F 1.