The diagonals of 2,7215' parallelogram are equal.
3. According to the question, AC+BD=36, so: OD+OC =1/2 (AC+BD) =18, CD = AB = 5, so the triangle circumference is: 18+5=23.
4. Because ABCD is a parallelogram, AD∨BC, thus AF∨EC, and because AF=EC, AECF is a parallelogram.
5. Because points E, F, G and H are the midpoint of AO, BO, CO and DO respectively, OE=OG, OF=OH, and the diagonal is bisected, it is a parallelogram.
6. Angle ABC = 70, BE bisects the angle ABC, so the angle EBC is 35. According to DF∨BE and DE∨BF, BEDF is a parallelogram with angle EBC= angle ADF = 35. Because the angle ABC= the angle ADC, we find the angle 1 = 35.
7. It is known that the quadrilateral AC'BCB'' is a parallelogram with angle ABC= angle B' and AB' = BC, and then it is known that the quadrilateral AC' BC is a parallelogram, so AB' = AC'.
8. Equal bottoms are equal in height, so the areas are equal. As long as we find a little p on l 1, the PBC area of the triangle is equal to the ABC area of the triangle.
9, right triangle AD, O, so from the Pythagorean theorem, AO= 13, so the diagonal of quadrilateral ABCD is equally divided, and the parallelogram ABCD is equally divided, so BC=AD= 12, and the area is AD*BD= 120.
10, prompt: use AD parallel and equal EF parallel and equal BC.
1 1, 6, a quadrilateral with equal sides is a parallelogram.
12, because sunlight is parallel, it is a parallelogram on the ground. According to the nature of parallelogram, its circumference is 2*(55+40)= 190. According to the nature of a right triangle, an angle of 30 corresponds to half of the hypotenuse, and its area is 1/2 (55 *).