`12km15m=12,015km`

`22km5m=22,005km`

`6m5dm=6,5m`

`35m5cm=35,05m`

`19m9mm=19,009m`

6 tấn 7 tạ = 6,7 tấn

16 tấn 25 kg=16,025 tấn

25 tạ 75kg =2575 kg

0,15 tạ = 15 kg

`5,9kg =5900 g`

\(2,6km^2=260hm^2\)

\(3275m^2=0,3275ha\)

\(5,2m^2=520dm^2\)

\(3,26dm^2=326cm^2\)

\(2,5cm^2=0,025dm^2\)

A = 10 + 15 + 20 + 25 + \(x\)

A = (10 + 20) + (15 + 25) + \(x\)

A = 30 + 40 + \(x\)

A = 70 + \(x\) 

6 : 31 = 0 dư 6 

?

4³ = 4.4.4 = 64

Em có nhầm đề ko nhỉ lớp 7 ko giải được bài này

\(Sai\) \(Thầy\) \(Ơi\)

a; \(x^3\) + 64 

= \(x^3\) + 4³

= (\(x+4\))(\(x^2\) - 4\(x\) + 16)

b; 2\(x^2\) - 4\(x\)

= 2\(x\)(\(x-2\))

c; 6\(x^2\)y + 4\(xy^2\) + 2\(xy\)

= 2\(xy\)(3\(x\) + 2y + 1)

a) x³ + 64

= x³ + 4³

= (x + 4)(x² − 4x + 16)

b) 2x² − 4x

= 2x(x - 2)

c) 6x²y + 4xy² + 2xy

= 2xy(3x + 2y + 1)

d) Sửa đề: x² − x + y − 2xy + y²

= x² − 2xy + y² − x + y

= (x − y)² − (x − y)

= (x − y)(x − y − 1)

5A:

b: \(47-\dfrac{\left(45\cdot24-5^2\cdot12\right)}{14}\)

\(=47-\dfrac{1080-25\cdot12}{14}\)

\(=47-\dfrac{1080-300}{14}=47-\dfrac{780}{14}=-\dfrac{61}{7}\)

d: \(2345-1000:\left[19-2\left(2\cdot1-18^2\right)\right]\)

\(=2345-1000:\left(19+2\cdot322\right)\)

\(=2345-\dfrac{1000}{19+644}=2345-\dfrac{1000}{663}=\dfrac{1553735}{663}\)

5B:

b: \(50-\left[\left(20-2^3\right)\right]:2+34\)

\(=84-\dfrac{20-8}{2}=84-6=78\)

c: \(20-\left[30-\left(5-1\right)^2\right]:3\)

\(=20-\dfrac{\left[30-4^2\right]}{3}\)

\(=20-\dfrac{14}{3}=\dfrac{46}{3}\)

d: \(205-\left[1200-\left(4^2-23\right)^3\right]:40\)

\(=205-\left[1200-\left(16-23\right)^3\right]:40\)

\(=205-\dfrac{\left[1200-\left(-7\right)^3\right]}{40}\)

\(=205-\dfrac{1200+343}{40}\)

\(=205-38,575=166,425\)

\(u_n=\dfrac{1}{2}\left(\dfrac{2}{1.3}+\dfrac{2}{3.5}+...+\dfrac{2}{\left(2n-1\right)\left(2n+1\right)}\right)\)

\(=\dfrac{1}{2}\left(1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+...+\dfrac{1}{2n-1}-\dfrac{1}{2n+1}\right)\)

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

Số hạng thứ \(2021\) là \(u_{2021}=\dfrac{2021}{2.2021+1}=\dfrac{2021}{4043}\)

   68313 - (200 + 313)

= 68313 - 200 -  313 

= (68313 - 313) -  200

= 68000 - 200

= 67800

= 68313 - 313 + 200

= 68000 + 200

= 68200

      A = 3 + 3² + 3³ + ... + 3²⁰¹⁵

     3A = 3² + 3³ + 3⁴ + ... + 3²⁰¹⁶

3A - A = 3² + 3³ + 3⁴ + ... + 3²⁰¹⁶

    2A    = 3² + 3³ + 3⁴ + ... + 3²⁰¹⁶ - (3 + 3² + 3³ + ... + 3²⁰¹⁵)

    2A =  3² + 3³ + 3⁴ + ... + 3²⁰¹⁶ - 3 - 3² - 3³ - ... - 3²⁰¹⁵

  2 A =  3 ²⁰¹⁶ - 3 + (3² - 3²) + (3³ - 3³) + ... + (3²⁰¹⁵ - 3²⁰¹⁵)

    2A =  3²⁰¹⁶ - 3 + 0 + 0 + ... + 0 + 0

    2A = 3²⁰¹⁶ - 3

2A + 3 = 3²⁰¹⁶ - 3 + 3 

 2A + 3 = 3²⁰¹⁶ - (3 - 3) = 3^4\(x\)

3²⁰¹⁶ = 3^4\(x\)

2016 = 4\(x\)

  \(x\) = 2016 : 4

  \(x=\) 504

Vậy \(x=504\)