Vd 3:

a) 9/10 > 5/42                                        b) -4/27 < 10/-73

Vd 4:

5/-6: -7/12; 5/8; 3/4

Vd 5:

x<y

Vd 6:

-16/27= -16/27> -16/29

Đặt A=\(\frac{6}{-7}\)+ \(\frac{9}{4}\). \(\frac{2}{15}\)- \(\frac{2}{14}\)

    A  = \(\frac{6}{-7}\)+ \(\frac{3}{10}\)- \(\frac{2}{14}\)

   A= \(\frac{-60}{70}\)+ \(\frac{21}{70}\)- \(\frac{10}{70}\)

A= \(\frac{-7}{10}\)

\(\text{Ta có :}P=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2015}}{2014+\frac{2013}{2}+...+\frac{1}{2014}}\)

\(\Rightarrow P=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2015}}{A}\)với \(A=2014+\frac{2013}{2}+...+\frac{1}{2014}\)

\(\Rightarrow A=1+\left(1+\frac{1}{2014}\right)+\left(1+\frac{1}{2013}\right)+\left(1+\frac{1}{2012}\right)+...+\left(1+\frac{2013}{2}\right)\)

\(\Rightarrow A=\frac{2015}{2}+\frac{2015}{3}+...+\frac{2015}{2014}+\frac{2015}{2015}\)

\(\Rightarrow A=2015.\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2014}+\frac{1}{2015}\right)\)

\(\text{Khi đó : }P=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2015}}{A}=\frac{\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2015}}{2015.\left(\frac{1}{2}+\frac{1}{3}+...+\frac{1}{2014}+\frac{1}{2015}\right)}\)

\(\Rightarrow P=\frac{1}{2015}\)

em chưa học bài này ạ

C= 3n-4n\1+2

C= n.(3-4)\ 3

C= n .-1\3

C= -n\3

chả bt đúng không 

a, xét \(\Delta AMN\) có: góc ngoài của \(\Delta AMN\)tại góc M là 110⁰

\(\Rightarrow\widehat{AMN}=180^0-110^0=70^0\)

Có \(\widehat{AMN}=\widehat{MBC}\left(=70^0\right)\)mà chúng ở vị trí so le trong

\(\Rightarrow MN//BC\)

b,xét \(\Delta ABC\)có:

\(\widehat{BAC}+\widehat{B}+\widehat{C}=180^0\)

\(\Rightarrow\widehat{BAC}=180^0-\left(70^0+65^0\right)\)

\(\Rightarrow\widehat{BAC}=45^0\)

Có \(M\in AB,N\in AC\)

\(\Rightarrow\widehat{BAC}=\widehat{MAN}=45^0\)