Bài V:

-ĐKXĐ: \(x\ne\pm1\).

\(\dfrac{m}{x-1}+\dfrac{x}{x+1}=\dfrac{x^2}{x^2-1}\)

\(\Leftrightarrow\dfrac{m\left(x+1\right)}{\left(x-1\right)\left(x+1\right)}+\dfrac{x\left(x-1\right)}{\left(x-1\right)\left(x+1\right)}=\dfrac{x^2}{\left(x-1\right)\left(x+1\right)}\)

\(\Rightarrow mx+m+x^2-x=x^2\)

\(\Leftrightarrow m\left(x+1\right)=x\)

\(\Leftrightarrow m=\dfrac{x}{x+1}\)

-Vì m,x nguyên:

\(\Rightarrow x⋮\left(x+1\right)\)

\(\Rightarrow\left(x+1-1\right)⋮\left(x+1\right)\)

\(\Rightarrow-1⋮\left(x+1\right)\)

\(\Rightarrow\left(x+1\right)\in\left\{1;-1\right\}\)

\(\Rightarrow x\in\left\{0;-2\right\}\) (nhận)

*\(x=0\Rightarrow m=\dfrac{x}{x+1}=\dfrac{0}{0+1}=0\)

\(x=-2\Rightarrow m=\dfrac{x}{x+1}=\dfrac{-2}{-2+1}=1\)

-Vậy với \(m=0\) thì \(S=\left\{0\right\}\)

         với \(m=1\) thì \(S=\left\{-2\right\}\)

a. Trọng lượng của vật là:

P=10.m= 10.15=150N

Trọng lực có phương thẳng đứng, chiều từ trên xuống dưới.b. c.Trọng lượng của vật là:

P= 10.m= 10.6=60N

Trọng lượng có phương thẳng, đứng chiều từ trên xuống dưới.

Vì vật đang đứng yên, nên chứng tỏ đã có 2 lực cân bằng tác dụng vào vật. Đó là trọng lực và lực nâng (P = Q)

Tỉ số giữa số cây của hai lớp 4B và 4C là:

1/2:3/4=2/3

Lớp 4C trồng được 28:1x3=84(cây)

Lớp 4B trồng được 84-28=56(cây)

Lớp 4A trồng được 3/4x56=42(cây)

9 will have to

10 must work

11 will you do - fail

12 will you do

13 were - would buy

14 were - would help

15 had - would travel

16 had - would go

17 would tell - were

18 knew - would speak

19 gets - will go

20 can play - is

21 isn't raining - will have

22 had - would finish

23 wouldn't do - were

24 didn't speak

25 would buy - had

26 weren't - would buy 

27 goes

28 will she go

29 would you do - were

30 were - would help

31 would you buy - were

32 would she do - were

33 will they do - become

34 would Ba go - had

35 had been - would have helped

36 had had - would have bought

37 hadn't bought - would have bought

38 would have been - hadn't rained

39 wouldn't have done

40 would have bought

41 would you do

42 would you have done

43 would you have done

44 would you have bought

45 has

46 would have come

III.

1 I will visit you

2 I would travel around the world

3 we will fail the final term test

4 you should take care of her

5 I would run away

6 we will go on a picnic

7 I would have got a good mark

8 he wouldn't be so fat now

9 I would kill it 

=>(X+X+....+X)+(2+4+...+20)=360

=>10X+(20+2)*10:2=360

=> 10X+110=360

=> 10X=360-110=250

=>X=250:10

=>X=25

   study well

K NHA

 CẢM ƠN CẢM BẠN NHIỀU

(x + 2) + (x + 4) + ... + (x + 20) = 360 (10 cặp)

=> (x + x + ... + x) + (2 + 4 + ... + 20) = 360

     20 số hạng x        20 số hạng

=> 20x + 20.(20 + 2) : 2 = 360

=> 20x + 220 = 360

=> 20x           = 140

=>     x           = 7

Vậy x = 7

\(\left(x+2\right)+\left(x+4\right)+...+\left(x+20\right)=360\)

\(\left(x+x+x+...+x\right)+\left(2+4+6+...+20\right)=360\)   ( 10 số x )

\(10x+\left(20+2\right).10:2=360\)

\(\Rightarrow10x+120=360\Rightarrow10x=360-120=240\)

\(\Rightarrow x=240:10=24\)

ok nha

A = 1/2 + 1/6 + 1/16 + ... + 1/4084441   có : 2021 - 1 + 1 = 2021 số

1 = 1/2021 + 1/2021 + ... + 1/2021   có 2021 số 

vậy 1 > A

\(\left|2x-3\right|=3-2x\)

\(ĐK:x\le\dfrac{3}{2}\)

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

\(\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{3}{2}\\0=0\left(đúng\right)\end{matrix}\right.\)

Vậy \(S=\left\{x\in R;x=\dfrac{3}{2}\right\}\)

Bài 1: 

a) Dấu hiệu: Điểm kiểm tra môn toán của 40 học sinh lớp 7A

số các giá trị: 40

b) số trung bình cộng: (4.2+5.7+6.7+7.7+8.8+9.6+10.3)/40=7,05

M₀= 8