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7 tháng 6 2018

\(A=\left(\frac{3}{5}+\frac{47}{13}-\frac{25}{8}+\frac{1}{8}-\frac{8}{13}+\frac{2}{5}\right)\times\frac{2014}{2015}\)

\(A=\left[\left(\frac{3}{5}+\frac{2}{5}\right)+\left(\frac{47}{13}-\frac{8}{13}\right)-\left(\frac{25}{8}-\frac{1}{8}\right)\right]\times\frac{2014}{2015}\)

\(A=\left[1+3-3\right]\times\frac{2014}{2015}\)

\(A=1\times\frac{2014}{2015}\)

\(A=\frac{2014}{2015}\)

1 tháng 6 2021
Sai bét thế mà cũng đòi chữa
5 tháng 3 2022

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!

30 tháng 1 2022

dễ thấy vế trái luôn>0 nên 6x>0=> x>0

x>0, bỏ dấu trị tuyệt đối ra ta đc 4x+10=6x

x=5

chúc bạn học giỏi, ăn Tết đc ngon, hehe -_-

HYC-30/1/2022

30 tháng 1 2022

Answer:

\(\left|x+1\right|+\left|x+2\right|+\left|x+3\right|+\left|x+4\right|=6x\)

Có \(\left|x+1\right|+\left|x+2\right|+\left|x+3\right|+\left|x+4\right|\ge0\)

\(\Rightarrow6x\ge0\)

\(\Rightarrow x\ge0\)

\(\Rightarrow x+1+x+2+x+3+x+4=6x\)

\(\Rightarrow4x+10=6x\)

\(\Rightarrow2x=10\)

\(\Rightarrow x=5\)

26 tháng 1 2019

\(3\left|x+1\right|=21\)

\(\left|x+1\right|=7\)

\(\Rightarrow\orbr{\begin{cases}x+1=7\\x+1=-7\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=6\\x=-8\end{cases}}\)

Vậy \(x\in\left\{-8;6\right\}\)

26 tháng 1 2019

\(3\left|x+1\right|=21\)

\(\Rightarrow\left|x+1\right|=7\)

\(\Rightarrow\hept{\begin{cases}x+1=7\\x+1=-7\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x=6\\x=-8\end{cases}}\)

21 tháng 12 2017

152,1:2,34=65

21 tháng 12 2017

152,1 : 2,34 = 65

24 tháng 12 2021

-16

24 tháng 12 2021

-16

19 tháng 1 2022

Bài 5 chứ nhỉ?

V.

1 When I came home,my mother was cooking dinner

2 My grandpa used to catch dangerous criminals

3 They had to wash the dishes after lunch

4 My father has got a beard and brown eyes

19 tháng 1 2022

My mother cooking dinner when I was came home

My grandpa used to catch dangerous criminals

They had to wash dishes the after lunch

My father has got a beard and brown eyes

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

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

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

\(=593.100.10+170.100\)

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

\(=100.6000=600000\)