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I
1.B
2.C
3.A
II
1.A , Used to
2.C Going
3.B .Housework
4.C. Subject
5.B. Good
III.
1. Many _homeless____ families have to live in tents
2. He was very _proud____ of the work he had done.
3. Freedom of _____speech__ is one of the fundamental rights.
4. His sense of __humor__ him from other students.
IV: Give the correct form/ tense of the verbs.
1. They asked us (not go) ...not to go... out alone at night.
2. The children were excited about (open) ..opening........ their presents.
3. She ..has just had........ (just have) dinner.
4. ko bk
V: Complete the second sentence so that it has a similar meaning to the first one.
1. '' How much do you think it will cost? '' he said to me.
- He asked me_how much I thought it would cost_
2. It takes minh 2 hours to do his homework every day.
- Minh spends _2 hours doing his homework every day
3,4,5 ko bk. Chỉ bk chừng đó thôi
1. He is used to------------ up early in the morning.
A. get B. getting C. have gotten D. got
2. The boy was kept indoors----------- naughty.
A. to be B. have been C. for being D. when he
3. I shall never forget-----------with you to Paris last year.
A. staying B. to staying C. to stay D. stayed
4. I am looking forward to -----------you.
A. having seen B. seeing C. to see D. all are wrong
5. I am always remember------------ off the lights before I leave my house.
A. turning B. to turn C. turned D. being turned
Áp dụng tính chất tỉ số ta có: \(\frac{a+b+d}{a+b+c+d}>\frac{a+b}{a+b+c}>\frac{a+b}{a+b+c+d}\left(1\right)\)
Tương tự: với b,c rồi cộng vế theo vế có ĐPCM
Lời giải:
Gọi biểu thức đã cho là $A$.
CM vế 1:
Ta có:
$\frac{a+b}{a+b+c}> \frac{a+b}{a+b+c+d}$
$\frac{b+c}{b+c+d}> \frac{b+c}{a+b+c+d}$
$\frac{c+d}{c+d+a}> \frac{c+d}{a+b+c+d}$
$\frac{d+a}{d+a+b}> \frac{d+a}{a+b+c+d}$
Cộng lại: $A> \frac{2(a+b+c+d)}{a+b+c+d}=2>1$
CM vế 2:
Ta thấy $\frac{a+b}{a+b+c}-\frac{a+b+d}{a+b+c+d}=\frac{-cd}{(a+b+c)(a+b+c+d)}< 0$ với $a,b,c,d>0$
$\Rightarrow \frac{a+b}{a+b+c}< \frac{a+b+d}{a+b+c+d}$
Hoàn toàn tương tự với các phân thức còn lại:
$\Rightarrow A< \frac{3(a+b+c+d)}{a+b+c+d}=3$
Ta có đpcm.