\(-1-\frac{1}{2}-\frac{1}{4}-\frac{1}{6}-.....-\frac{1}{1024}\)

\(=-1-\left(1-\frac{1}{2}\right)-\left(\frac{1}{2}-\frac{1}{4}\right)-.....-\left(\frac{1}{512}-\frac{1}{1024}\right)\)

\(=-1-\left(1-\frac{1}{1024}\right)\)

\(=-1-\frac{1023}{1024}\)

\(=-\frac{2047}{1024}\)

thi violympic mà tra kiểu này thì có mà thi chơi chứ hiểu gì

sai đề x+z chứ x+2 =72 thì x = 70 rùi

mk làm giup bn nhé

x/2 = y/4 ; y/5 = z/7

bn có MSC(4;5) = 20 => x/10 = y/20 = z/28

mà x+z =72

k = 72/(10+28)  = 36/19

x = 10.k

y = 20.k

z = 28.k

\(\frac{a}{4}-\frac{1}{b}=\frac{3}{4}\)

\(\Rightarrow\frac{1}{b}=\frac{3}{4}-\frac{a}{4}\)

\(\Rightarrow\frac{1}{b}=\frac{3-a}{4}\)

Áp dụng công thức tích chung tỷ = tích ngoại tỷ

=> b.(3 - a) = 1 . 4

=> 3.b - ab = 4

=> 3.b = 4 - a.b 

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