17. 丨-10/3 丨 > -π >-3.3

18.x=- 1，y=2，z=0

19.( 1) Original formula =7+4= 1 1

What is the final absolute value? Six? I can't see clearly, I think it's 6)

Original formula =7/2*6=2 1

20.( 1)-(-3) = 3 > 丨 -2 丨 =2

(2)-(-4)=4=4 = 4 = 4

(3)-4/5=- 12/ 15- 1

The reciprocal of 2 1. (1)a is-A. On the right side of 0, the absolute distance from 0 to A is equal.

(2) From the question, we can know that 买 a 买+买 [the ancient or Latin modern names of animals and plants] 买 =20, and a is negative.

Then a=- 10

(3) I can't see the last few words clearly and can't answer.