Bg 

Ta có: C = 1 - 2 + 3 - 4 + 5 -…+ 2011 - 2012 + 2013

Có 2012 số và 1 số cuối cùng là 2013.

=> C = (1 - 2) + (3 - 4) + (5 -…) + (2011 - 2012) + 2013

Bây giờ thì có 2012 ÷ 2 = 1006 cặp và số 2013

=> C = -1 + (-1) +…+ (-1) + 2013

=> C = -1.1006 + 2013

=> C = -1006 + 2013

=> C = 1007

Vậy C = 1007.

C = 1 - 2 + 3 - 4 + ... + 2011 - 2012 + 2013

= (1 - 2) + (3 - 4) + ... + (2011 - 2012) + 2013   (có tất cả 1006 cặp)

= -1 + (-1) + ... + (-1) + 2013

= -1 . 1006 + 2013

= 1007

Vậy C = 1007.

Gọi số gấu là a ; số hổ là b ; số chim công là c

Ta có a + b + c = 25

=> 2 x (a + b + c) = 25 x 2

=> 2 x a + 2 x b + 2 x c = 50 (1)

b = 4 x a

Lại có Hổ có 4 chân ; gấu có 4 chân ; công có 2 chân

Ta có : 4 x a + 4 x b + 2 x c = 70

=> 2 x (2 x a + 2 x b + c) = 70

=> 2 x a + 2 x b + c = 35 (2)

Lấy (1) trừ (2) theo vế ta có 

2 x a + 2 x b + 2 x c - (2 x a + 2 x b + c) = 50 - 35

=> 2 x a + 2 x b + 2 x c - 2 x a - 2 x b - c = 15

=> 2 x c - c = 15

=> c = 15

Khi đó a + b = 25 - 15 

=> a + b = 10

Lại có b = 4 x a

=> a + 4 x a = 10 

=> 5 x a = 10

=> a = 2

=> b = 10 - 2 = 8

Vậy số gấu là 2 ; số sư tử là 8 con ; số chim công là 15 con

đúng

1)

O a b c d m A B C D

2)

   Có

Vì A,C,D thẳng hàng và B,C,D thẳng hàng

Nên A,B,C,D thẳng hàng

=> 4 điểm A,B,C,D cùng nằm trên một đường thẳng 

   Vậy AC và BD trùng nhau

???????

Nếu bạn muốn người khác tôn trọng mình thì đừng cố tỏ ra mình là một người VÔ VĂN HÓA !!!!

Trả lời :

B = - 2 + 4 - 6 + 8 - ... - 18 + 20

= - 2 + (4 - 6) + (8 - 10) + ... + (16 - 18) + 20

= - 2 - 2 - 2 - ... - 2 + 20

= - 2 . 9 + 20

= - 18 + 20

= 2

Bằng 10 nha

Ex1 : Give the correct form of the verb in present simple and present countinous :

1. Susie (not ) ________doesn't____________ ( be ) at a girl*s school . 

2 Susie ( study ) ________________studies___ for three hours a week . 

3. The students ( do) ______are doing________ judo in the gym now .

4._____Is_____ Mr . Lee ( have ) __having________ lunch with his students in the canteen at present 

5. Mr . Van ( teach ) ________teaches________ Physics at my school .

 6. Poppy ( not eat  ) ______________isn't eating__ dinner , she is phoning a friend .

7. I ( do ) ______am doing______ my math homework at the moment ,but I ( not understand  ) __am not understanding____________ the first  question

Ex2 : Reorder the sentences : 

1 . often / on sundays / has / breakfast / in bed / Mike . =>Mike often has breakfast in bed on sundays

2 . is / on friday evenings / at home  / Kate / never . =>Kate is never at home on friday evenings

3 . speaks / in our engkish lessons / always / our teach / english . =>Our teacher always speaks english in our english lessons

4 . go for / They / on / a walk / Saturday mornings . =>they go for a walk on saturday mornings

5 . not / watching / i am / sport on tv / keen on . =>I am not keen on watching sport on tv

6 . is / music / Ba / with / listening / his friends / to / now . =>Ba is listening to music with his friends now

7 . there / shelves / any / our classroom / in / aren*t .=>There aren't any shelves in our classroom

8 . the / there / teacher*s desk / a computer / aren*t / a / on =>There aren't a computer on the teacher desk

Ex1 : Give the correct form of the verb in present simple and present countinous :

1. Susie (not ) ____doesn't being________________ ( be ) at a girl*s school . 

2 Susie ( study ) ____studies_______________ for three hours a week . 

3. The students ( do) __are doing____________ judo in the gym now .

4.____Is______ Mr . Lee ( have ) __having________ lunch with his students in the canteen at present 

5. Mr . Van ( teach ) ____teaches____________ Physics at my school .

 6. Poppy ( not eat  ) ____isn't eating____________ dinner , she is phoning a friend .

7. I ( do ) __am doing__________ my math homework at the moment ,but I ( not understand  ) ___am not understand___________ the first  question

Ex2 : Reorder the sentences : 

1 . often / on sundays / has / breakfast / in bed / Mike . 

Mike often has breakfast in bed on Sundays

2 . is / on friday evenings / at home  / Kate / never

Kates is never at home on Friday evenings. 

3 . speaks / in our engkish lessons / always / our teach / english

Our teach English always speaks in our english lessons. 

4 . go for / They / on / a walk / Saturday mornings . 

They go for a walk on Saturday mornings

5 . not / watching / i am / sport on tv / keen on

I'm not keen on watching. sport on TV 

6 . is / music / Ba / with / listening / his friends / to / now .

Ba is listening music with his friends now 

7 . there / shelves / any / our classroom / in / aren*t

There aren't any shelve in our classroom.

8 . the / there / teacher*s desk / a computer / aren*t / a / on 

There aren't a computer on the teacher's desk 

Ta có: \(2\left(2x^2+2x+1\right)=\left(5x+2\right)\sqrt{x^2+1}\)

\(\Leftrightarrow4\left(2x^2+2x+1\right)^2=\left(5x+2\right)^2\left(x^2+1\right)\)

\(\Leftrightarrow16x^4+32x^3+32x^2+16x+4=25x^4+20x^3+29x^2+20x+4\)

\(\Leftrightarrow9x^4-12x^3-3x^2+4x=0\)

\(\Leftrightarrow\left(9x^4-12x^3\right)-\left(3x^3-4x\right)=0\)

\(\Leftrightarrow x\left(3x-4\right)\left(3x^3-1\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}x=0\\x=\frac{4}{3}\end{cases};x^3=\frac{1}{3}}\)

\(\Leftrightarrow x\in\left\{0;\frac{1}{\sqrt[3]{3}};\frac{4}{3}\right\}\)

Bài của Huyen Trang bổ sung thêm tập xác định R nữa là ok!

Ta có: 68.(-77) - 77.22 

       =  -77( 68 + 22 )

       =  - 77 . 100 = -7700

Trả lời :

68 . (- 77) - 77 . 22

= (- 68) . 77 - 77 . 22

= 77 . (- 68 - 22)

= 77 . (- 90)

= - 6930

bài này lớp 8 học rồi nhé , bạn đặt đúng lớp ạ

Ta có : \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=1< =>\left(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}\right)^2=1\)

\(< =>\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2}+\frac{2}{ab}+\frac{2}{bc}+\frac{2}{ca}=1\)

\(< =>\frac{1}{a^2}+\frac{1}{b^2}+\frac{1}{c^2}+\frac{2}{ab}+\frac{2}{bc}+\frac{2}{ca}-\frac{2}{bc}+\frac{1}{a^2}+1=1\)

\(< =>\left(\frac{1}{a^2}+\frac{1}{a^2}\right)+\left(\frac{2}{bc}-\frac{2}{bc}\right)+\frac{1}{b^2}+\frac{1}{c^2}+\frac{2}{ab}+\frac{2}{ca}=1-1=0\)

\(< =>\frac{2}{a^2}+\frac{2}{ab}+\frac{1}{b^2}+\frac{1}{c^2}+\frac{2}{ca}=0< =>\left(\frac{1}{a}+\frac{1}{c}\right)^2+\left(\frac{1}{a}+\frac{1}{b}\right)^2=0\)

\(< =>\hept{\begin{cases}\frac{1}{a}+\frac{1}{c}=0\\\frac{1}{a}+\frac{1}{b}=0\end{cases}< =>\hept{\begin{cases}\frac{1}{c}=-\frac{1}{a}\\\frac{1}{b}=-\frac{1}{a}\end{cases}}< =>b=c=-a}\)(*)

Thế (*) và giả thiết \(\frac{1}{a}+\frac{1}{b}+\frac{1}{c}=1< =>\frac{1}{a}+\frac{1}{-a}+\frac{1}{-a}=1\)

\(< =>\frac{1-1-1}{a}=1< =>-\frac{1}{a}=1< =>a=-1\)

Khi đó ta được \(b=c=-\left(-1\right)=1< =>\hept{\begin{cases}a=-1\\b=1\\c=1\end{cases}}\)

Nên \(P=\left(a-2b+4c\right)^{2019}=\left(-1-2+4\right)^{2019}=1^{2019}=1\)