2.a, cho A=172 −174 +176 −178 +...+1798 −17100 . CMR :A<150
b,Giả sử có 2015 số nguyên dương a1,a2,a3,...,a2015thỏa mãn : 1a1 +1a2 +1a3 +1a4 +...+1a2015 =1008 . CMR:có ít nhất 2 trong 2015 số nguyên dương đã cho = nhau
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`@` `\text {Ans}`
`\downarrow`
\(\text{ A = }\dfrac{1}{4\times8}+\dfrac{1}{8\times12}+\dfrac{1}{12\times16}+...+\dfrac{1}{172\times176}\)
\(\text{A = }\dfrac{1}{4}\times\left(\dfrac{4}{4\times8}+\dfrac{4}{12\times16}+...+\dfrac{4}{172\times176}\right)\)
\(\text{A = }\dfrac{1}{4}\times\left(\dfrac{1}{4}-\dfrac{1}{8}+\dfrac{1}{12}-\dfrac{1}{16}+...+\dfrac{1}{172}-\dfrac{1}{176}\right)\)
\(\text{A = }\dfrac{1}{4}\times\left(\dfrac{1}{4}-\dfrac{1}{176}\right)\)
\(\text{A = }\dfrac{1}{4}\times\dfrac{43}{176}\)
\(\text{A = }\dfrac{43}{704}\)
Đáp số: `\text {A =} 43/704.`
172. The water was so cold that the children could not take a swim.
The water wasn’t ___WARM ENOUGH FOR THE CHILDREN TO TAKE A SWIM____
173. It’s two months since I last spoke to her.
I haven’t ___SPOKEN TO HER FOR 2 MONTHS_
174. “Turn down the radio, Nam.” , his father said.
Nam’s father __ASKED HIM TO TURN DOWN THE RADIO_______
175. Lan will be seventeen next week.
It’s ___LAN'S SEVENTEENTH BIRTHDAY NEXT WEEK____
176. How long is it since you bought the car ?
When _DID YOU BUY THE CAR?__
177. Nam began to collect stamps in 2000.
Nam has ____COLLECTED STAMPS SINCE 2000____
172. The water was so cold that the children could not take a swim.
The water wasn’t too cold for the children to take a swim_________________________________________________________
173. It’s two months since I last spoke to her.
I haven’t spoken to her for two months_______________________________________________________________
174. “Turn down the radio, Nam.” , his father said.
Nam’s father told Nam to turn down the radio____________________________________________________________
175. Lan will be seventeen next week.
It’s Lan's seventeen birthday next week____________________________________________________________________
176. How long is it since you bought the car ?
When did you buy the car__________________________________________________________________
177. Nam began to collect stamps in 2000.
Nam has collected stamps since 2000_______________________________________________________________
170.I’d like meet a ghost, but I have never seen one.
171.We moved here in 1983. We have been here a long time now.
172. I have worked for a computer company for a year. That was after college.
173.Martin has been to Greece five times. He loves the place.
174.Why are you working so hard these days ?
- Because I am going to buy a car, so I’m saving as much as I can.
175.I’m trying to move this cupboard, but it’s very heavy. - Well, I will help you then
176 Do you mind not leaving your papers all over the table ?
- Oh, sorry. I’ll take them all with me when I go
177.Could I have a word with you, please ?
- Sorry. I’m in a big hurry. My train will leave in 15 minutes.
178.I’ve decided to repaint this room. -Oh, have you ? What color will you paint?
Chúc bạn học tốt
1 D
2 C
3 C
4 D
5 B
6 D
7 D
8 B
9 A
10 D
11 D
12 C
13 C
14 B
15 C
16 B
174/ Ron has to complete his writting before Tuesday. a has to b before c complete d writting =>writing 175/ Are you interested for photography? a photography b interested c for=>in d are 176/ Your advice are exactly right. a exactly b right c are=>is d advice 177/ Sue like going to the cinema. a going b the c cinema d like =>likes 178/ Sunday is an wonderful day for me. a for b an=>a c is d wonderful 179/ I can’t come to the cinema. I’ve got too many homework. a too b come c I've d many=>much 180/ She is too young for understand the problem. a understand b is c too d for=>to 181/ Most birds sings in the morning. a in b sings=>sing c birds d the 182/ Cook some water, and pour it into the cup. a cook=>boil b into c some d pour 183/ Helen know more than three foreign languages. a foreign b language c more d know=>knows 184/ Milk is poor in vitamin A and B2. a vitamin=>vitamins b in c is d poor 185/ There is a lot of hotels in that city a hotels b lot c is=>are d in 186/ He goes to the National Library every Saturdays. a the b every c Saturdays =>saturday d goes 187/ After listen to the news on the radio, I leave for school a the news b listen=>listening c for d on 188/ Is there anything good in TV tonight? a TV b anything c in=>on d is 189/ I’m fond in coffee a fond b in=>of c I'm d coffee