Ta có A = 75 ( 4^ 2013+4^2012+...+4^2+4+1)+25

              = 75( 4^ 2013+4^2012+...+4^2+4) +75 +25

              = 75[4(4^2012+...+4^2+4+1)] +100 

              = 300(4^2012+...+4^2+4+1) +100 

              = 100 [3(4^2012+...+4^2+4+1) + 1 ] chia hết cho 100 (Đ.P.C.M)

1. B. Knew => Known

2. B. More => most

3. D. To play => playing

bài này mà là lớp 3 ak`?

=.= cái này phải xác định có thật hay k có thật ở HT hay QK nữa ak =.=

Thể tích cái hộp đó là:

               15 x 15 x 15 = 3375 (cm3)

 Diện tích cần sơn là:

               15 x 15 x 5 = 1125 (cm2)

                         Đáp số: a/ 3375 cm3

                                     b/ 1125 cm2

Cái này..... khó giải thích

\(\frac{5}{28}+\frac{5}{70}+\frac{5}{130}+\frac{5}{208}+\frac{5}{304}=\frac{5}{3}.\left(\frac{3}{4.7}+\frac{3}{7.10}+\frac{3}{10.13}+\frac{3}{13.16}+\frac{3}{16.19}\right)\)

\(=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{10}+...+\frac{1}{16}-\frac{1}{19}\right)=\frac{5}{3}.\left(\frac{1}{4}-\frac{1}{19}\right)\)

\(=\frac{5}{3}.\frac{15}{74}=\frac{25}{74}\)

\(2^{x+3}+2^x=144\) 

\(\Rightarrow2^x\left(2^3+1\right)=144\) 

\(\Rightarrow2^x.9=144\) 

\(\Rightarrow2^x=\frac{144}{9}=16=2^4\) 

Vậy \(x=4\)

\(x+2x+3x+...+9x=459-3^2\) 

\(\Rightarrow9x+\left(1+2+3+...+9\right)=450\) 

\(\Rightarrow9x+\frac{\left[\left(9+1\right).9\right]}{2}=450\) 

\(\Rightarrow9x+45=450\) 

\(\Rightarrow9x=450-45\) 

\(\Rightarrow x=\frac{450-45}{9}=\frac{405}{9}=45\)

I. chọn đáp án đúng

1. Which word has the second stress?

A.History                  B.Biology                                   c.Gepgraphy                    D.B,C are correct

2. Which word has the first stress?

A.often                       B.hungry                                    C.survey                         D. All are correct

II. Chia động từ trong ngoặc

1. I'd like to join (join) your club

III. viết lại câu sau cho đúng nghĩa

1. Do you have a better refrigerator than hí?

Is this the best refrigerator you have?

2. My house is the oldest house on the street

No house is older than my house on the street.

IV. điền từ vào chõ tróng

California is the most (1) famous state the USA. It isn't the (2) biggest state: that Alaska. But it is (3) the largest population and it's certainly the muos important state of.(4) the US economy. It's richer than(5) most contries in the world. The coast has most (6) of the best climates in the USA: It (7) is warmer and dryer than most places. Some people would also say(8) it's the most  beautiful ! But California has some problems (9); Losangeles has one of the worst crime rates of any US city