DT
0
K
Khách
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
Các câu hỏi dưới đây có thể giống với câu hỏi trên
TQ
1
LM
31 tháng 10 2017
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
CL
12 tháng 10 2017
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
TL
12 tháng 3 2017
ta có :
\(\dfrac{bz-cy}{a}=\dfrac{cx-az}{b}=\dfrac{ay-bx}{c}=\dfrac{bxz-cyz}{ax}=\dfrac{cxy-azy}{by}=\dfrac{ayz-bxz}{cz}\)áp dụng tính chất dãy tỉ số bằng nhau, ta có:\(\dfrac{bzx-cyx}{ax}=\dfrac{cxy-azy}{by}=\dfrac{ayz-bxz}{cz}=\dfrac{bzx-cyx+cxy-azy+ayz-bxz}{ax+by+cz}=0\)
suy ra : bz-cy=0 \(\Rightarrow bz=cy\Rightarrow\dfrac{y}{b}=\dfrac{z}{c}\left(1\right)\)
cx-az=0\(\Rightarrow cx=az\Rightarrow\dfrac{x}{a}=\dfrac{z}{c}\left(2\right)\)
ay-bx=0\(\Rightarrow ay=bx\Rightarrow\dfrac{x}{a}=\dfrac{y}{b}\left(3\right)\)
từ (1), (2) và (3) suy ra: \(\dfrac{x}{a}=\dfrac{y}{b}=\dfrac{z}{c}\)
12 tháng 3 2017
Ta có: \(\dfrac{bz-cy}{a}\)= \(\dfrac{cx-az}{b}\)=\(\dfrac{ay-bx}{c}\)
\(\Rightarrow\dfrac{abz-acy}{a^2}=\dfrac{bcx-baz}{b^2}=\dfrac{cay-cbx}{c^2}\)(nhân cả tử và mẫu với mẫu của phân số)
\(=\dfrac{abz-acy+bcx-baz+cay-cbx}{a^2+b^2+c^2}\) (t/c của dãy tỉ số bằng nhau)
(đến đây ta thấy tử = 0 vì chúng là các số đối nhau, abz-baz; acy-cay; bcx-cbx)
\(=\dfrac{0}{a^2+b^2+c^2}\)
\(\Rightarrow\)\(\dfrac{bz-cy}{a}\)= 0 (mà để là một phân số thì mẫu phải khác 0) suy ra a khác 0 vậy bz-cy=0 \(\Rightarrow bz=cy\Rightarrow\dfrac{z}{c}=\dfrac{y}{b}\)(1)
tương tự \(\dfrac{cx-az}{b}\)=0 suy ra \(\dfrac{x}{a}=\dfrac{z}{c}\) từ 1 và 2 suy ra điều phải c/m\(\)
25 tháng 7 2018
Error Identification.
1.JeanJean cloth waswas made completecomplete=>completely fromfrom cotton.
2.WouldWould you like comecome=>to come and visitvisit me nextnext summer?
3.Ao Dai waswas frequentlyfrequently worn by both manman=>men and womenwomen.
4.Wearing uniformsWearing uniforms helphelp=>helps students feelfeel equal in many waysways.
5.WearingWearing uniforms encouragesencourages students to be to be proud aboutabout =>of their school.
6.She wisheswishes she cancan =>could speak English as wellwell asas her teacher.
7.I seldom gogo to aa football match.I'm not very interestinginteresting=>interested inin football.
8.A newnew style of jeans havehave=>has just been introducedintroduced in in the USA.
9.InIn the 18th18thcentury, jean cloth waswas made completelycompletely byby=>from cotton.
10.Mr.Brown is interestedinterested in to go shopping to go shopping=>going shopping everyevery Sunday.
11.I wishwish I havehave=>had a new watch. MineMine is too too old.
12.Emma used toused to lie onon the beach when she liveslives=>lived by the seaby the sea.
13.WearingWearing uniforms encourageencourage=>encourages the students to beto be proud of theirtheir schools.
14.How longlong havehave you learninglearning=>learnt EnglishEnglish?
15.Ao dai waswas frequentfrequent=>frequently worn worn by both men and womenboth men and women.
TH
25 tháng 7 2018
Error Identification.
1.Jean cloth was made complete=>completely from cotton.
2.Would you like come=>to come and visit me next summer?
3.Ao Dai was frequently worn by both man=>men and women.
4.Wearing uniforms help=>helps students feel equal in many ways.
5.Wearing uniforms encourages students to be proud about =>of their school.
6.She wishes she can =>could speak English as well as her teacher.
7.I seldom go to a football match.I'm not very interesting=>interested in football.
8.A new style of jeans have=>has just been introduced in the USA.
9.In the 18th century, jean cloth was made completely by=>from cotton.
10.Mr.Brown is interested in to go shopping=>going shopping every Sunday.
11.I wish I have=>had a new watch. Mine is too old.
12.Emma used to lie on the beach when she lives=>lived by the sea.
13.Wearing uniforms encourage=>encourages the students to be proud of their schools.
14.How long have you learning=>learnt English?
15.Ao dai was frequent=>frequently worn by both men and women.