Đúng, cần phải nắm chắc đó bạn !

Vì nó rất quan trọng !

a; Áp dụng công thức:

     \(\dfrac{a}{b}\) > \(\dfrac{a+m}{b+m}\) (a; b; m \(\in\) N' a > b)

Ta có: \(\dfrac{999}{556}\) > \(\dfrac{999+1}{556+1}\) = \(\dfrac{1000}{557}\)

b; \(\dfrac{-2}{15}\) < 0

   \(\dfrac{-10}{-11}\) = \(\dfrac{-10:-1}{-11:-1}\) = \(\dfrac{10}{11}\) > 0

\(\dfrac{-2}{15}\) < 0 < \(\dfrac{-10}{-11}\)

 Vậy \(\dfrac{-2}{15}\) < \(\dfrac{-10}{-11}\)

\(\widehat{xAB}+\widehat{ABy}=45^o+135^o=180^o\)

Mà 2 góc này ở vị trí trong cùng phía 

⇒ Ax//By (1)

\(\widehat{CBA}+\widehat{CBy}+\widehat{ABy}=360^o\)

\(\Rightarrow\widehat{CBy}=360^o-135^o-75^o=150^o\)

\(\widehat{BCz}+\widehat{CBy}=30^o+150^o=180^o\)

Mà 2 góc này ở vị tri trong cùng phia 

⇒ By//Cz (2)

Từ (1) và (2) => Ax//Cz 

a) Ta có:

\(\widehat{xOy}+\widehat{OAz}=150^o+30^o=180^o\)

Mà 2 góc này ở vị trí trong cùng phía

\(\Rightarrow zz'//Oy\)

b) OM là phân giác của \(\widehat{xOy}\Rightarrow\widehat{MOA}=\dfrac{1}{2}\widehat{xOy}=\dfrac{1}{2}\cdot150^o=75^o\) 

\(\widehat{OAz'}+\widehat{OAz}=180^o\) (kề bù)

\(\Rightarrow\widehat{OAz'}=180^o-30^o=150^o\)

ON là phân giác của \(\widehat{OAz'}\Rightarrow\widehat{OAN}=\dfrac{1}{2}\widehat{OAz'}=\dfrac{1}{2}\cdot150^o=75^o\)

\(\Rightarrow\widehat{MOA}=\widehat{OAN}=75^o\) 

Mà 2 góc này ở vị trí đồng vị 

⇒ OM//AN 

Bạn tham khảo !!!

Tet is a national festival in Vietnam,  many Vietnamese people love it. Tet is celebrated in the January of lunar calendar to welcome the new year. Before Tet, people buy food, fruits, drink, flowers, and the most important is the peach blossom or kumquat tree. Children are bought new clothes by their parents.  On New Year's Eve, all of the family members gather to give each other the best wishes and have a meal. During Tet, people can go to the parks, stadiums to see fireworks, it is very beautiful. Children can receive lucky-money from parents and relatives. I staying at home to watch the New Year's comedies, it makes me laugh a lot.  On the next day, people go to the temple to thank the ancestors, Buddha who helped everyone in the old year. In short, I really love Tet, and I hope that Tet will always be an important festival for Vietnamese people. 

TRời ơi, thanks bạn nha

Đề bài yêu cầu gì em?

tìm số hữu tỉ a và b

Bạn xem lại đề nhé.

có gì đó ko đúng ?

\(\left(2x-3y\right).5xy\\ =5xy.2x+5xy.\left(-3y\right)\\ =10x^2y-15xy^2\)

(2x - 3y) - 5xy

=5xy . 2x + 5xy - (-3y)

= 10 x^2 y - 15xy^2

\(\dfrac{x+2022}{2020}+\dfrac{x-2016}{2018}=\dfrac{x+2021}{2019}+\dfrac{x-2019}{2021}\\ \Rightarrow\left(\dfrac{x+2022}{2020}-1\right)+\left(\dfrac{x-2016}{2018}+1\right)=\left(\dfrac{x+2021}{2019}-1\right)+\left(\dfrac{x-2019}{2021}+1\right)\\ \Rightarrow\dfrac{x+2}{2020}+\dfrac{x+2}{2018}-\dfrac{x+2}{2019}-\dfrac{x+2}{2021}=0\\ \Rightarrow\left(x+2\right)\left(\dfrac{1}{2020}+\dfrac{1}{2018}-\dfrac{1}{2019}-\dfrac{1}{2021}\right)=0\\ \)

\(\Rightarrow x+2=0\) ( Vì: \(\dfrac{1}{2020}+\dfrac{1}{2018}-\dfrac{1}{2019}-\dfrac{1}{2021}>0\) )

\(\Rightarrow x=-2\)

suy ra x = -2