A có nghĩa khi 4-x^2 khác 0 và x^2 - 2x khác 0

<=> x khác 0

x khác 2 và x khác -2

1c  2a    3a   4a   5d

8.Her telephone number doesn't knew

9.The children home will be brought by my students

10.I was sent a present last week

11. We were gave more information 

C

A

A

is cleaned

are served

are brought

are given

are spoken

làm lại ok chưa bn

CuO+2HCl->CuCl₂+H₂O

n CuO=0,1 mol

m HCl=21,9g-> nHCl=0,6 mol

lập tỉ lệ =>HCl dư

n HCl dư=0,4 mol =>M HCl=0,4.36,5=14,6g

=>C%HCl dư=

=>m CuCl2=0,1.135=13,5g

=>C%CuCl2=