1. Among the following figures, the centrally symmetric figure is ().

1。

2. In order to know the weight of 400 eighth-grade students in a school, 50 students were randomly selected for statistical analysis. In this question, it generally refers to ().

A 400 students b 50 students C 400 students weight d 50 students weight.

3. The following formula is a fraction ()

A B C D

4. As shown in the figure, in the diamond ABCD, diagonal AC and BD intersect at point O, and the following statement is wrong ().

A.ab∑DC b . AC = BD c.ac⊥bd d . OA = oc

5. As shown in the figure, the diagonal AC and BD of rectangular ABCD intersect at points O, CE∨BD, DE∨AC, and if AC=4, the perimeter of quadrilateral code ()

A.4 B. 6 C. 8 D. 10

6. As shown in Figure 4, AB CD is a square, G is any point on BC (except the endpoint), DE⊥AG is at point E, BF∑de, AG is at point F, and the following conclusion is not necessarily true ().

A.△AED?△BFA B . DE-BF = EF C . AF-BF = EF D . DE-BG = FG

Figure 4, Figure 5, Figure 6

7. Among the scores of,, and, the number of the simplest score is _ _ _ _. ( )

1。

8. As shown in the figure, E and F are the points on the side CD and AD of the square ABCD, respectively.

And CE=DF, AE and BF intersect at point o, and the following conclusions are drawn:

⑴ AE=BF ⑵ AE⊥BF ⑶ AO=OE

(4)sδAOB = s quadrilateral DEOF, and the correct one is ().

A 4 B 3 C 2 D 1

Fill in the blanks (2 points for each question, 20 points for * * *)

9. In the diamond-shaped ABCD, the diagonal AC and BD are 6cm and 10cm respectively, so the area of the diamond-shaped ABCD is.

10. When x=, the value of the score is 0.