Sửa đề; CMR: Với mọi số thực x,y,z luôn có:
\(\left|x+y-z\right|+\)\(\left|y+z-x\right|+\)\(\left|x+z-y\right|+\)\(\left|x+y+z\right|\)\(\ge2\left(\left|x\right|+\left|y\right|+\left|z\right|\right)\)
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16 in(tham khảo c16)
18D
19B
20A
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22 has worked
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29 Nam doesn't eat sweet any more
Hoặc
Nam used to eat a lot of sweet when he was a child but he never eats sweet now
30 Mrs.Lien asked me to give her the handbook
31 History isn't as difficult as English
32 Hoa's hobby is different from Nam's hobby
1 satisfied => satisfaction
2 of => for
3 about => on
4 to use => using
5 for => to