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.