Because the quadrilateral ABCD is a right-angled trapezoid, the angle B is equal to 90 degrees.

So AD is parallel to BC, that is, PD is parallel to QC.

To make the quadrangle PDCQ a parallelogram, PD should be parallel and equal to QC.

Suppose that after x seconds, the quadrilateral PDCQ is a parallelogram, which is derived from the meaning in the question:

24-X=3X

Solution: X=6

That is, the six-second quadrilateral PQCD is a parallelogram.

Isosceles trapezoid: It takes 7 seconds. There are many ways to ask this question. You can make a vertical line from point D to BC and cross BC at point E. If PD equals 24-7= 17 after 7 seconds, QC=7 times 3 = 2 1 1, and 21-kloc-0/7 equals 4, then CE=2.

That's it, absolutely self-created, absolutely correct, please adopt me, thank you, hehe, you can ask me any questions in the future, and all subjects in Chinese and English can be counted.