Tên : Thư

2k6

nice to meet you

mk là người đeo kính nha

234 x 49 + 51 x 234

= 234 x ( 49 + 51 )

= 234 x 100

= 23400

   234x49+51x234

=234x(49+51)

=234x100

=23400

tk mk và kb với mk nha

234x49+51x234=23.400

nha

1+1=2

2+2 =4

........................còn phần dưới mik ko bít

2

4

O

S

E 

A

2

4

O

S

E

A

Đặt A=\(\dfrac{1}{11}\)+\(\dfrac{1}{12}\)+\(\dfrac{1}{13}\)+...\(\dfrac{1}{69}\)+\(\dfrac{1}{70}\)

         =(\(\dfrac{1}{11}\)+\(\dfrac{1}{12}\)+\(\dfrac{1}{13}\)+...\(\dfrac{1}{19}\)+\(\dfrac{1}{20}\))+(\(\dfrac{1}{21}\)+\(\dfrac{1}{22}\)+\(\dfrac{1}{23}\)+...+\(\dfrac{1}{29}\)+\(\dfrac{1}{30}\))+(\(\dfrac{1}{31}\)+\(\dfrac{1}{32}\)+\(\dfrac{1}{33}\)+...+\(\dfrac{1}{59}\)+\(\dfrac{1}{60}\))+...+\(\dfrac{1}{70}\)

Nhận xét:

\(\dfrac{1}{11}\)+\(\dfrac{1}{12}\)+\(\dfrac{1}{13}\)+...+\(\dfrac{1}{19}\)+\(\dfrac{1}{20}\)>\(\dfrac{1}{20}\)+\(\dfrac{1}{20}\)+...+\(\dfrac{1}{20}\)=\(\dfrac{10}{20}\)=\(\dfrac{1}{2}\)

\(\dfrac{1}{21}\)+\(\dfrac{1}{22}\)+\(\dfrac{1}{23}\)+...+\(\dfrac{1}{29}\)+\(\dfrac{1}{30}\)>\(\dfrac{1}{30}\)+\(\dfrac{1}{30}\)+...+\(\dfrac{1}{30}\)=\(\dfrac{10}{30}\)=\(\dfrac{1}{3}\)

\(\dfrac{1}{31}\)+\(\dfrac{1}{32}\)+\(\dfrac{1}{33}\)+...+\(\dfrac{1}{59}\)+\(\dfrac{1}{60}\)>\(\dfrac{1}{60}\)+\(\dfrac{1}{60}\)+...+\(\dfrac{1}{60}\)=\(\dfrac{30}{60}\)=\(\dfrac{1}{2}\)

=>A>\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{2}\)+\(\dfrac{1}{61}\)+...+\(\dfrac{1}{69}\)+\(\dfrac{1}{70}\)>\(\dfrac{1}{2}\)+\(\dfrac{1}{3}\)+\(\dfrac{1}{2}\)=\(\dfrac{4}{3}\)

=>A>\(\dfrac{4}{3}\)

Vậy: \(\dfrac{1}{11}\)+\(\dfrac{1}{12}\)+\(\dfrac{1}{13}\)+...+\(\dfrac{1}{69}\)+\(\dfrac{1}{70}\)>\(\dfrac{4}{3}\) (ĐPCM)

Thấy đúng cho 1 tick và 1 follow nha!

Chúc bạn học tốt!

Cái này phải là cộng nhé bn, mk lm r

\(\frac{1}{1\cdot2}+\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{99\cdot100}\)

\(=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{99}-\frac{1}{100}\)

\(=1-\frac{1}{100}=\frac{99}{100}\)

\(=\frac{99}{100}\)

\(\frac{99}{100}\)

\(583.931+69\left(170+583\right)+31.170\)

\(=583.931+69.170+69.583+31.170\)

\(=593\left(931+69\right)+170\left(69+31\right)\)

\(=593.100.10+170.100\)

\(=100\left(593.10+170\right)\)

\(=100.6000=600000\)

162:3^2x-4 = 2

3^2x-4 = 162 : 2 = 81 = 3^4

=> 2x-4=4

=> 2x=4+4=8

=> x=8:2=4

3^x.3^3=81

3^x=81:3^3=3 =3^1

=> x=1

k mk nha

162:3^2x-4=2

3^2x-4=162:2

3^2x-4=81

<=> 3^2x-4=3⁴

=> 2x-4=4

2x=4+4

2x=8

x = 8:2

x = 4

3^x.3³=81

3^x.27=81

3^x=81:27

3^x=3

<=> x=1

a,\(162:3^{2x-4}=2\)

\(3^{2x-4}=81\)

\(3^{2x-4}=3^4\)

\(\Rightarrow2x-4=4\)

\(2x=8\)

\(x=4\)

b, \(3^x.3^3=81\)

\(3^x.3^3=3^4\)

\(3^x=3^1\)

\(\Rightarrow x=1\)

2

...

bạch là gì vậy?

a) 136 - x : 48 = 27,8 + 92

136 - x : 48 = 119,8

x ; 48 = 136 - 119,8

x : 48 = 16,2

x = 16,2 * 48

x = 777,6

b) 43,7 - x - 8,92 = 0,348 * 19

43,7 - x - 8,92 = 6,612

43,7 - x = 6,612 + 8,92

43,7 - x = 15,532

x = 43,7 - 15,532

x = 28,168

Mk nhanh nhất đó

a 135-x:4=27,8+92

=> 125-x:4=119.8

=> x:4=119,8+125

=> x:4=244.8

=> x=244,8:4

=> x=61,12

b 43,7-x-8,92=0,248x19

=> x= 30.068

a) 136 - X : 48 = 27,8 + 92

    136 - X : 48 = 119,8

         136 - X   = 119,8 x 48

          136 - X = 5750,4

          X         = 136 - 5750,4

                  X =   - 5614,4