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.Find out corect one mistake in A,B,C or D of each sentece and then correct
1. He slept=>was sleeping in his room when the fire alarm rang.
2.Shall=>Will you close the window for me, please?
3. He gets up early in order to reviewing=>review lessons before school
4. The ambulance will be there for=>in about ten minutes
5. I've been leaning English since=>for 4 years
Gọi \(A=\dfrac{1}{2}+\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+...+\dfrac{1}{x}=\dfrac{1023}{1024}\)
\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+...+\dfrac{1}{x}=\dfrac{1023}{1024}\)
VẬy x là một lũy thừa của 2. Đặt x = 2y , ta có:
\(A=\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+...+\dfrac{1}{2^y}\)
\(\Rightarrow2A=1+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+...+\dfrac{1}{2^{y-1}}\)
\(\Rightarrow2A-A=1+\dfrac{1}{2}-\dfrac{1}{2^2}+\dfrac{1}{2^3}-\dfrac{1}{2^4}+...+\dfrac{1}{2^{y-1}}-\left(\dfrac{1}{2}+\dfrac{1}{2^2}+\dfrac{1}{2^3}+\dfrac{1}{2^4}+...+\dfrac{1}{2^8}\right)\)
\(=A-\dfrac{1}{2^y}\)
Vậy \(1-\dfrac{1}{2^y}=\dfrac{1023}{1024}\Leftrightarrow\dfrac{1}{2^y}=\dfrac{1}{1024}\Leftrightarrow2^y=1024\Rightarrow x=1024\)
Vậy x = 1024
1,
a) 3,2x +(-12)x +2,7=-4,9 b)-5,6x+2,9x-3,86=-9,8
=>3,2x+(-12)x=-4,9-2,7 =>-5,6x+2,9x=-9,8+3,86
=>3,2x+(-12)x=-7,6 =>-5,6x+2,9x=-5,94
=>x[3,2+(-12)]=-7,6 =>x[(-5,6)+2,9]=-5,94
=>2x=-7,6=>x=-7,6:2=-3,8 =>-2,7x=-5,94=>x=(-5,94):(-2,7)=2,2
1.iron→→ironed
2.look⇒⇒looked
3.wash⇒⇒washed
4.return⇒⇒returned
5.borrow⇒⇒borrowed
6.borrow⇒⇒borrowed
7.play⇒⇒played
8.decide⇒⇒decided
9.take⇒⇒took
10.think⇒⇒thought
11.talk⇒⇒talked
12.ride⇒⇒rode
13.live⇒lived
1.iron\(\Rightarrow\Rightarrow\)ironed
2.look⇒⇒looked
3.wash⇒⇒washed
4.return⇒⇒returned
5.borrow⇒⇒borrowed
6.borrow⇒⇒borrowed
7.play⇒⇒played
8.decide⇒⇒decided
9.take⇒⇒took
10.think⇒⇒thought
11.talk⇒⇒talked
12.ride⇒⇒rode
13.live\(\Rightarrow\Rightarrow\)lived
1. The teacher always welcomes new student.→ New student is always welcomed.
2. People speak E all over the world→ English is spoken all over the world.
3.Thomas Edison invented the photograph in 1877→ The photograph was invented in 1877.
4. The police found two children in the forest→ Two children was found in the forest.
5. They will send your order as soon as possible→ Your order will be sent as soon as possible.
6. The scientists are studying the problem carefully→ The problem is being studied carefully.
7. Pat Murphy was riding the horse→ The horse was being ridden by Pat Murphy.
8. The police have just arrested the robbers→ The robbers have just been arrested.
9. Sue told us she had born her baby→ They have been told that Sue had born her baby.
10. They can use this room after 5 p.m→ This room can be used after 5 p.m.
11. He spoke French very fluently→ French was spoken very fluently.
12. They sell many goods in this market→ Many goods are sold in this market.
13. We learn a lot of subjects at school→ A lot of subjects are learnt at school.
14. Minh rode his bike to school→ The bike was rode to school by Minh.
15. My neighbor planted trees in his garden→ Trees were planted in my neighbor`s garden
Ủa câu này bạn phải đăng lên chuyên mục Toán chứ?