có đừng đăng linh tinh nha

còn mk nè bn 

khos vay ai lam

lớp 6 đấy

A xin lỗi mình viết sai đề để mình viết lại

(0,25 - 3/4) : 2/3 + (-1/2)^2

\(\left(0,25-\frac{3}{4}\right)\div\frac{2}{3}+\left(\frac{-1}{2}\right)^2\)²

\(=\left(\frac{1}{4}-\frac{3}{4}\right)\times\frac{3}{2}+\frac{1}{4}\)

\(=\frac{-1}{2}\times\frac{3}{2}+\frac{1}{4}\)

\(=\frac{-3}{4}+\frac{1}{4}\)

\(=\frac{-2}{4}=\frac{-1}{2}\)

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