1. In quadrilateral ABCD, AB is perpendicular to CD and its vertical foot is O, ao >；; C0, Bo & gtDO, verifying AD+BC & gt；; AB+CD.2. If point P is a point in the parallelogram ABCD, connect AP, BP, CP, DP, and then connect diagonal AC. If the area of triangle APB is 20 and the area of triangle APD is 15, try to find the area of triangle APC. 3. It is known that the quadrilateral ABCD is an isosceles trapezoid, AB//CD, and the diagonal AC and BD intersect at O. If ∠ AOB = 60, E, F and G are the midpoints respectively, it is proved that △EFG is an equilateral triangle. 4. Rectangular AE=A 1E 1, AF = A 1E 1, and find ef//e15. It is known that the diagonal of □AH⊥BCD intersects with point O, ef intersects with AD at point E, BC intersects with F and g. O, and AE⊥BD intersects with E, BE:ED= 1:3, ∠AOB=4, and 1) and ∠. 7. It is known that in Rt△ABC, ∠BAC is a right angle, ∠ Abd. M is the midpoint of BC, which proves that FH=2AM9. Known quadrilateral AB=CD is isosceles trapezoid, AB = CD, AD∨BC, DE∨CA, BA intersection extension line is verified at point E: edab = eabd 10. In the parallelogram ABCD, the line segments EF∨BC, BE, CF intersect at points S, AE, DF intersect at points P. Verification: SP∨AB.

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