2. Yes. At this time, its four corners are right angles.
3. yes. At this time, it gets an equilateral quadrilateral with right angles.
4. Angle A=60 degrees, angle B=30 degrees.
5.( 1) angle BAD=60, angle ABC= 120.
(2)AB = 6 cm, AC = 10.39 cm.
6. We can know AB=CD by angle ABD= angle DBC= angle ADB, and AB=BC in the same way, so that AD is parallel to BC, and the quadrilateral ABCD is a diamond.
7.45 degrees
8. Rectangular. All four corners are right angles.
9.45 degrees.
10. Quadrilateral Amen Amen, EFCG are quadrilaterals with equal sides.
11.ab× DH = 2ao× od = 2aAbd area, and DH=2.4CM can be obtained.
12.B(- root number12,0), C (0 0,2), d (root number12,0)
13. The quadrilateral EFMN is a square.
14.3 species.
15.ADE are all equal to BAF.
16.BO = 2OD, which must be passed.
17. There are countless kinds. Just keep the two paths perpendicular to each other and cross the center of the square.