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Bài 8:

a: Ta có: \(M=\dfrac{2\sqrt{x}-9}{x-5\sqrt{x}+6}-\dfrac{\sqrt{x}+3}{\sqrt{x}-2}+\dfrac{2\sqrt{x}+1}{\sqrt{x}-3}\)

\(=\dfrac{2\sqrt{x}-9-x+9+2x-4\sqrt{x}+\sqrt{x}-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)

\(=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}\)

b: Thay \(x=11-6\sqrt{2}\) vào M, ta được:

\(M=\dfrac{3-\sqrt{2}+1}{3-\sqrt{2}-3}=\dfrac{4-\sqrt{2}}{-\sqrt{2}}=-2\sqrt{2}+1\)

1 tháng 10 2021

Bài 8:

a) \(M=\dfrac{2\sqrt{x}-9-\left(\sqrt{x}+3\right)\left(\sqrt{x}-3\right)+\left(2\sqrt{x}+1\right)\left(\sqrt{x}-2\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}\)

\(=\dfrac{2\sqrt{x}-9-x+9+2x-3\sqrt{x}-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}=\dfrac{x-\sqrt{x}-2}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}=\dfrac{\left(\sqrt{x}-2\right)\left(\sqrt{x}+1\right)}{\left(\sqrt{x}-2\right)\left(\sqrt{x}-3\right)}=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}\)

b) \(M=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}=\dfrac{\sqrt{11-6\sqrt{2}}+1}{\sqrt{11-6\sqrt{2}}-3}=\dfrac{\sqrt{\left(3-\sqrt{2}\right)^2}+1}{\sqrt{\left(3-\sqrt{2}\right)^2}-3}=\dfrac{4-\sqrt{2}}{-\sqrt{2}}=1-2\sqrt{2}\)

c) \(M=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}=3\)

\(\Leftrightarrow3\sqrt{x}-9=\sqrt{x}+1\Leftrightarrow2\sqrt{x}=10\Leftrightarrow\sqrt{x}=5\Leftrightarrow x=25\left(tm\right)\)

d) \(M=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}< 1\)

\(\Leftrightarrow\sqrt{x}+1< \sqrt{x}-3\Leftrightarrow1< -3\left(VLý\right)\)

Vậy \(S=\varnothing\)

e) \(M=\dfrac{\sqrt{x}+1}{\sqrt{x}-3}=1+\dfrac{4}{\sqrt{x}-3}\in Z\)

\(\Rightarrow\sqrt{x}-3\inƯ\left(4\right)=\left\{-4;-2;-1;1;2;4\right\}\)

Kết hợp đk:

\(\Rightarrow x\in\left\{1;16;25;49\right\}\)

25 tháng 10 2021

Bài 8:

a) \(A=\dfrac{\sqrt{a}-1}{\sqrt{a}}.\dfrac{\sqrt{a}+1+\sqrt{a}-1}{\left(\sqrt{a}-1\right)\left(\sqrt{a}+1\right)}=\dfrac{2\sqrt{a}}{\sqrt{a}\left(\sqrt{a}+1\right)}=\dfrac{2}{\sqrt{a}+1}\)

b) \(A=\dfrac{2}{\sqrt{a}+1}=\dfrac{2}{\sqrt{3-2\sqrt{2}}+1}=\dfrac{2}{\sqrt{\left(\sqrt{2}-1\right)^2}+1}=\dfrac{2}{\sqrt{2}-1+1}=\dfrac{2}{\sqrt{2}}=\sqrt{2}\)

Bài 9:

\(pt\Leftrightarrow\sqrt{\left(3x+1\right)^2}=2\)\(\Leftrightarrow\left|3x+1\right|=2\)

\(\Leftrightarrow\left[{}\begin{matrix}3x+1=2\\3x+1=-2\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}3x=1\\3x=-3\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{1}{3}\\x=-1\end{matrix}\right.\)

30 tháng 11 2021

Bài 10:

a: =254-254+135=135

AH
Akai Haruma
Giáo viên
25 tháng 6 2021

Bài 8.9.10 của câu 14 hay 15 bạn?

Câu 15:

1: Ta có: \(\dfrac{1}{1-\sqrt{2}}-\dfrac{1}{1+\sqrt{2}}\)

\(=\dfrac{1+\sqrt{2}-1+\sqrt{2}}{\left(1-\sqrt{2}\right)\left(1+\sqrt{2}\right)}\)

\(=-2\sqrt{2}\)

2: Ta có: \(\dfrac{1}{\sqrt{5}+1}+\dfrac{1}{\sqrt{5}-1}\)

\(=\dfrac{\sqrt{5}-1+\sqrt{5}+1}{\left(\sqrt{5}+1\right)\left(\sqrt{5}-1\right)}\)

\(=\dfrac{2\sqrt{5}}{4}=\dfrac{\sqrt{5}}{2}\)

Bài 10:

a: \(\overrightarrow{AB}+\overrightarrow{BO}+\overrightarrow{OA}\)

\(=\overrightarrow{AO}+\overrightarrow{OA}=\overrightarrow{0}\)

b: \(\overrightarrow{OA}+\overrightarrow{BC}+\overrightarrow{DO}+\overrightarrow{CD}\)

\(=\overrightarrow{OA}+\overrightarrow{DO}+\overrightarrow{BD}\)

\(=\overrightarrow{OA}+\overrightarrow{BO}=\overrightarrow{BA}\)

26 tháng 10 2021

b: \(BC=\sqrt{89}\left(cm\right)\)

\(\sin\widehat{B}=\dfrac{5\sqrt{89}}{89}\)

\(\Leftrightarrow\widehat{B}\simeq32^0\)

\(\widehat{C}=58^0\)

NV
19 tháng 3 2022

8a.

\(\lim\limits_{x\rightarrow1^+}f\left(x\right)=\lim\limits_{x\rightarrow1^+}\left(3x^2-5x+1\right)=3-5+1=-1\)

\(\lim\limits_{x\rightarrow1^-}f\left(x\right)=\lim\limits_{x\rightarrow1^-}\left(-3x+2\right)=-3+2=-1\)

\(\Rightarrow\lim\limits_{x\rightarrow1^+}f\left(x\right)=\lim\limits_{x\rightarrow1^-}f\left(x\right)\Rightarrow\) hàm có giới hạn tại \(x=1\)

Đồng thời \(\lim\limits_{x\rightarrow1}f\left(x\right)=-1\)

b.

\(\lim\limits_{x\rightarrow2^+}f\left(x\right)=\lim\limits_{x\rightarrow2^+}\dfrac{x^3-8}{x-2}=\lim\limits_{x\rightarrow2^+}\dfrac{\left(x-2\right)\left(x^2+2x+4\right)}{x-2}\)

\(=\lim\limits_{x\rightarrow2^+}\left(x^2+2x+4\right)=12\)

\(\lim\limits_{x\rightarrow2^-}f\left(x\right)=\lim\limits_{x\rightarrow2^-}\left(2x+1\right)=5\)

\(\Rightarrow\lim\limits_{x\rightarrow2^+}f\left(x\right)\ne\lim\limits_{x\rightarrow2^-}f\left(x\right)\Rightarrow\) hàm ko có giới hạn tại x=2

NV
19 tháng 3 2022

9.

\(\lim\limits_{x\rightarrow0^+}f\left(x\right)=\lim\limits_{x\rightarrow0^+}\dfrac{x^2+mx+2m+1}{x+1}=\dfrac{0+0+2m+1}{0+1}=2m+1\)

\(\lim\limits_{x\rightarrow0^-}f\left(x\right)=\lim\limits_{x\rightarrow0^-}\dfrac{2x+3m-1}{\sqrt{1-x}+2}=\dfrac{0+3m-1}{1+2}=\dfrac{3m-1}{3}\)

Hàm có giới hạn khi \(x\rightarrow0\) khi:

\(\lim\limits_{x\rightarrow0^+}f\left(x\right)=\lim\limits_{x\rightarrow0^-}f\left(x\right)\Rightarrow2m+1=\dfrac{3m-1}{3}\)

\(\Rightarrow m=-\dfrac{4}{3}\)

24 tháng 7 2021

refer

1. like/dinner/house/would/have/tonight/you/to/my/at/?
Would you like to have dinner at my house tonight?

2.detective/parents/going/movie/this afternoon/we/see/with/are/a/our/to/.
We are going to see a detective movies with our parents this afternoon.

3.watching/prefers/to/brother/books/TV/my/reading.
My brother prefers watching TV and reading to books.

4.daughter / best/kinds/does /like/what/TV program/your /of/?
What kind of program does your daughter like best?

5. showing/local cinema/is/horror film / the/a/there/next week/at.
There is horror film showing at that local cinema next week.

6.durians /and/my/ like/much/does/I/very/father/so
I like durians very much so does my father.

7.went/she/stomachache/the doctor's/ an/Lan/because/awful to/ had.
Lan's went to the doctor's because she had an awful stomache.

8.have/the/farm/often/them/vegatables/from/dirt/on.
Vegetables from the farm of ten have dirt on time.

9.in/work/will/do/all/ the/machines/for/the/future/us.
In the future, machines will do all the work for us.

10.it/hours/about/two/Hoa Binh/to takes /by /get/to/couch.
It 's take us about to hours to get to Hoa Binh by couch.

24 tháng 7 2021

1 Would you like to have dinner at my house tonight?

2 We are going to see a detective movie with our parents this afternoon

3 My brother prefers watching TV to reading books

4 What kinds of TV program does your daughter like best?

5 There is a horror film showing at the local cinema next week

7 I like durians very much and so does my father

8 Vegetables often have dirt from the farm on them

9 Machines will do all the work for us in the future

10 It's takes about 2 hours to get to HoaBinh by coach