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DCBAC？ DDBAA

Fill in the blanks: (X+3)(X-3)

X=3

1

(3,- 1)

- 1

1/3 or 5/3

Answer: 17. 1+√3

18.( 1) BD = DC, FD = ED, CF = BE, and point D is the midpoint of BC line.

(2) Omission

19( 1)A is higher than B.

(2)6.97 meters

20? y=X2-2X-3

2 1? (1) omitted

(2) The radius is 5, and CE=4.8.

22~24(3)① See the figure.

24(3)② Existence (-2/3, √3/3)(-2/3, √3)