\(\frac{4}{9}:\left(x+0,4\right)=\frac{2}{3}=>\left(x+0,4\right)=\frac{4}{9}:\frac{2}{3}=>\left(x+0,4\right)=\frac{2}{3}=>x=\frac{2}{3}-0,4=>x=\frac{4}{15}\)

vậy \(x=\frac{4}{15}\)

\(\left|\frac{2}{7}-x\right|=1\frac{1}{3}=\orbr{\begin{cases}\left|\frac{2}{7}-x\right|=\frac{4}{3}\\\left|\frac{2}{7}-x\right|=-\frac{4}{3}\end{cases}}=>\orbr{\begin{cases}x=\frac{2}{7}-\frac{4}{3}\\x=\frac{2}{7}+\frac{4}{3}\end{cases}}=>\orbr{\begin{cases}x=-\frac{22}{21}\\x=\frac{34}{21}\end{cases}}\)

vậy \(\orbr{\begin{cases}x=-\frac{22}{21}\\x=\frac{34}{21}\end{cases}}\)

13 They've finished (do) their homework__doing

14 They had their house ( paint) before Tet holiday__painted

15 I advised him ( wait) for me at the airport__waiting

16 Would you mind (help) me with this work?__helping
17 Do you smell something (burn) in the chicken ?__burning

18 Mother requests her daughter not (come) back home late__come

19 We  shall have the grass (cut) tomorrow__cutting

20 They noed lots of sheep(graze) in green meadows___

21 When I'm tired , I enjoy (watch) TV . It's relaxing__watching

22 Would you (have) something to eat?_have
23 It started (rain)  an hour ago. Has it stopped (rain) yet?___rained__raining
24 My family is trying ( decide) where to go on holiday_decided

25 our teacher made me (answer) all the questions__answered

26 I've enjoy (meet) you . I hope (see) you again____meeting__see

27 I hate (see) a child (cry)__to see_crying

28 they prefer (play) in swimming pool all day___playing

29 the refuse(go) out on trips if it's too hot___to go

30 i used (smoke) 20 cigarettes a day , but now I give up (smoke)____smoked__smoking

31 We decided ( rent) a house with a swimming pool____

32 can you help me ( get ) the dinner ready ?__getting
33 when we arrived , the people next door invited us (have) a drink with them____having

34 We began (talk) about next year's holiday two months ago____talking

35 I remember (lock) the door when I left but forgot (shut) the window_______locked_shutting

36 He agrees (start) the job as soon as possible____started

37 I finished (read) the book and went to bed_____reading

38 My teachers always expected me (do)  well in exams_____to do

39 Let me ( pay) for the meal . You paid last time___paying

40 It's difficult (get) used to (eat) with chopsks_____got_eating

A = 2+2²+2³+....+2⁶⁰

A= (2+2²)+(2³+2⁴)+...+(2^59+2^60)

A=2(2+1)+2^3(2+1)+....+2^59(2+1)

A=2.3+2^3.3+...+2^59.3

A=3(2+2^3+....+2^59)

Vì 3 chia hết cho 3 => A chia hết cho 3

mà 105 chia hết cho 3

=> A chia hết cho 105

Ta có : A = 2 + 2² + 2³ + 2⁴ + 2⁵ + 2⁶ + 2⁷ + 2⁸ + ... + 2⁵⁷ + 2⁵⁸ + 2⁵⁹ + 2⁶⁰

=  (2 + 2² + 2³ + 2⁴) + (2⁵ + 2⁶ + 2⁷ + 2⁸) + ... + (2⁵⁷ + 2⁵⁸ + 2⁵⁹ + 2⁶⁰)   (Có 15 cặp)

= 2(1 + 2 + 2² + 2³) + 2⁵(1 + 2 + 2² + 2³) + ... + 2⁵⁷(1 + 2 + 2² + 2³)

= 2.15 + 2⁵.15 + ... + 2⁵⁷.15 

= 15(2 + 2⁵ + ... + 2⁵⁷) \(⋮\)15 (1)

Lại có A = 2 + 2² + 2³ + 2⁴ + 2⁵ + 2⁶  + ... +  2⁵⁸ + 2⁵⁹ + 2⁶⁰

             =  (2 + 2² + 2³) + (2⁴ + 2⁵ + 2⁶) + ... +  (2⁵⁸ + 2⁵⁹ + 2⁶⁰)  

             = 2(1 + 2 + 2²) + 2⁴(1 + 2 + 2²) + ... + 2⁵⁸(1 + 2 + 2²)

             = 2.7 + 2⁴.7 + ... + 2⁵⁸.7

             = 7(2 + 2⁴ + ... + 2⁵⁸) \(⋮\)7

=> \(A⋮7\)(2)

Vì ƯCLN(15;7) = 1

Từ (1) (2) =>  \(A⋮15.7\Rightarrow A⋮105\left(\text{đpcm}\right)\)

a. \(2a^2+5ab-3b^2-7b-2\)

\(=\left(2a^2+6ab+2a\right)-\left(ab+3b^2+b\right)-\left(2a+6b+2\right)\)

\(=2a\left(a+3b+1\right)-b\left(a+3b+1\right)-2\left(a+3b+1\right)\)

\(=\left(2a-b-2\right)\left(a+3b+1\right)\)

b. \(2x^2-7xy+x+3y^2-3y\)

\(=\left(2x^2-xy\right)-\left(6xy-3y^2\right)+\left(x-3y\right)\)

\(=x\left(2x-y\right)-3y\left(2x-y\right)+\left(x-3y\right)\)

\(=\left(x-3y\right)\left(2x-y\right)+\left(x-3y\right)\)

\(=\left(x-3y\right)\left(2x-y+1\right)\)

c. \(6x^2-xy-2y^2+3x-2y\)

\(=\left(6x^2+3xy\right)-\left(4xy-2y^2\right)+\left(3x-2y\right)\)

\(=3x\left(2x+y\right)-2y\left(2x+y\right)+\left(3x-2y\right)\)

\(=\left(3x-2y\right)\left(2x+y\right)+\left(3x-2y\right)\)

\(=\left(3x-2y\right)\left(2x+y+1\right)\)

đổi ra phân số hộ nhé

378 x X = 105

          X = \(\frac{105}{378}\)

          X = \(\frac{5}{18}\)

Ta có BĐT : \(a.b\le\left(\frac{a+b}{2}\right)^2\forall a,b\). Do đó :

\(x^3.\left(16-x^3\right)\le\left(\frac{x^3+16-x^3}{2}\right)^2=\left(\frac{16}{2}\right)^2=64\)

Dấu "=" xảy ra \(\Leftrightarrow x^3=16-x^3\)

\(\Leftrightarrow x^3=8\Leftrightarrow x=2\)

Vậy GTLN của \(x^3\left(16-x^3\right)\) là \(64\) khi \(x=2\)

P=a²⁰²¹+b²⁰²¹+c²⁰²¹

P=(a+b+c)²⁰²¹

mà a+b+c = 1

=> P= 1²⁰²¹=1

Gọi các góc của tam giác đó là: A; B; C (A;B;C khác 0)

Ta có: A/1=B/2=C/3 và A + B+ C=180* (tổng 3 góc trong tam giác)

Áp dụng tc dãy tso = nhau, ta có: 

A/1=B/2=C/3=A+B+C/1+2+3=180/6=30

=> A/1 = 30*(30x1)(dpcm)

=> B/2 = 60* (30x2)(dpcm)

=> C/3= 90* (30x3)(dpcm)

Gọi số đó các góc lần lượt là a,b,c ( cm )

Điều kiện : a,b,c > 0

Vì các góc tỉ lệ lần lượt với 1 ; 2 ; 3 nên \(\frac{a}{1}=\frac{b}{2}=\frac{c}{3}\)( 1 )

Xét \(\Delta\)có tổng số đo các góc là 180^o ( định lí ) ( 2 )

Từ ( 1 ) và ( 2 ) ta áp dụng tính chất của dãy tỉ số bằng nhau ta có :

\(\frac{a}{1}=\frac{b}{2}=\frac{c}{3}=\frac{a+b+c}{1+2+3}=\frac{180^o}{6}=30^o\)

\(\Rightarrow\hept{\begin{cases}\frac{a}{1}=30^o\\\frac{b}{2}=30^o\\\frac{c}{3}=30^o\end{cases}}\)\(\Rightarrow\hept{\begin{cases}a=30^o\\b=60^o\\c=90^o\end{cases}}\)

2 từ xin chào bằng Tiếng Anh: hello, hi

2 từ tạm biệt bằng Tiếng Anh: goodbye, so long

k mình nha

- xin chào: hello; Hi!

- tạm biệt: goodbye; farewell

\(\text{Thùng thứ hai chứa số lít dầu là:}\)

        \(180\times\frac{1}{2}=90\left(l\right)\)

\(\text{Cả hai thùng chứa số lít dầu là:}\)

         \(180+90=270\left(l\right)\)

                       \(\text{Đáp số:}\)\(270\)\(l\)

Thùng thứ hai chứa : 

180 x 1/2 = 90 ( l ) 

Cả hai thùng chứa  : 

180 + 90 = 270 ( l )