1. 1，x？ -4x+42、2√5

x？ -4x+4x-4 II。 1-3 CCB.

Third, 1, x-6. 2. (1)2x+8 .(2) Known: AB=2x+8, B=x? -4. find the value of a.

3.( 1) can be analyzed from different angles, such as: ① the average deviation rate of student A is 16%, and that of student B is11%; (2) The extreme deviation rate of student A is 7%, and that of student B is16%; ③ The minimum deviation rate of student A is 13%, and that of student B is 4%; ④ The maximum deviation rate of students A and B is 20%; ⑤ A students' ability to estimate the number of words has not improved significantly, while B students' ability to estimate the number of words has improved significantly.

(2) It can be analyzed from different angles. For example: ① From the average deviation rate, it is predicted that the average deviation rate of classmate A is 16%, and the estimated number of words is between 84- 1 16; The average deviation rate of student B is 1 1%, and the estimated number of words is 89 ~11; ② Prediction of median deviation rate: The median deviation rate of student A is 15%, and the estimated number of words is between 85- 1 15; The median deviation rate of B students is 10%, and the estimated number of words is between 90- 1 10; ③ Prediction from the variation of deviation rate: There is no obvious trend characteristic of a student's deviation rate, and there are many prediction methods. For example, the average value of the maximum and minimum deviation rate is 16.5%, and the estimated number of words is between 84 and 1 16 or 83 and 1 17. B students' deviation rate is

4 、( 1)a= 15，b=0. 16。 (2) 144 。 (3) 1080 (person)

5, BE=CF reason omitted. (hint: just prove △ Abe △ ACF. )