mik học lớp 5

Ta có : B=(1/5-1/5)-(3/7-3/7)+(5/9-5/9)-(2/11-2/11)+(7/13-7/13)-9/16

B=-9/16

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0-\frac{9}{16}\)

\(B=-\frac{9}{16}\)

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\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\) 

\(=\frac{1}{5}-\frac{1}{5}-\frac{3}{7}+\frac{3}{7}+\frac{5}{9}-\frac{5}{9}-\frac{2}{11}+\frac{2}{11}+\frac{7}{13}-\frac{7}{13}-\frac{9}{16}\) 

\(=0+0+0+0+0-\frac{9}{16}\) 

\(=\frac{-9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{1}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0+0+0+0+0-\frac{9}{16}\)

\(B=-\frac{9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(=0+0+0+0-\frac{9}{16}\)

\(=\frac{-9}{16}\)

Vậy \(B=\frac{-9}{16}\)

1/5 - 3/7 + 5/9 - 2/11 + 7/13 - 9/16 -7/13 + 2/11 - 5/9 +3/7 -1/5

= ( 1/5-1/5) + (-3/7 +3/7 ) + (5/9 - 5/9 ) + (-2/11+2/11 ) + ( 7/13 - 7/13 ) - 9/16

= 0 + 0 + 0 + 0 + 0 +0 - 9/16

= -9/16

\(\dfrac{1}{5}-\dfrac{3}{7}+\dfrac{5}{9}-\dfrac{2}{11}+\dfrac{7}{13}-\dfrac{9}{16}-\dfrac{7}{13}+\dfrac{2}{11}-\dfrac{5}{9}+\dfrac{3}{7}-\dfrac{1}{5}\)

\(=\)\(\left(\dfrac{3}{7}+\dfrac{-3}{7}\right)+\left(\dfrac{1}{5}-\dfrac{1}{5}\right)+\left(\dfrac{5}{9}-\dfrac{5}{9}\right)+\left(\dfrac{-2}{11}+\dfrac{2}{11}\right)+\left(\dfrac{7}{13}-\dfrac{7}{13}\right)+\dfrac{9}{16}\)

\(=0+0+0+0+0+\dfrac{9}{16}\)

\(=\dfrac{9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0-\frac{9}{16}\)

\(B=-\frac{9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0+0+0+0-\frac{9}{16}\)

\(B=0-\frac{9}{16}\)

\(B=-\frac{9}{16}\)

\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)

\(B=\frac{1}{5}+\left(-\frac{3}{7}\right)+\frac{5}{9}+\left(-\frac{2}{11}\right)+\frac{7}{13}+\left(-\frac{9}{16}\right)+\left(\frac{-7}{13}\right)+\frac{2}{11}+\left(\frac{-5}{9}\right)+\frac{3}{7}+\left(-\frac{1}{5}\right)\)

\(B=\left(\frac{1}{5}+\frac{-1}{5}\right)+\left(\frac{-3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}+\frac{-5}{9}\right)+\left(\frac{7}{13}+\frac{-7}{13}\right)+\frac{-9}{16}\)

\(B=0+0+0+0+\frac{-9}{16}\)

\(B=-\frac{9}{16}\)

Vậy \(B=\frac{-9}{16}\)

\(B=\left(\frac{3}{7}+-\frac{3}{7}\right)+\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{5}{9}+\frac{5}{9}\right)+\left(\frac{2}{11}+-\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0+0+0+0+0+\frac{9}{16}\)

\(B=0+\frac{9}{16}\)

\(B=\frac{9}{16}\)

\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)

\(B=0+0+0+0+0+\frac{9}{16}=\frac{9}{16}\)

Kết quả 1: Tính

Kết quả 2: Tính

\(B=\dfrac{1}{5}-\dfrac{3}{7}+\dfrac{5}{9}-\dfrac{2}{11}+\dfrac{7}{13}-\dfrac{9}{16}-\dfrac{7}{13}+\dfrac{2}{11}-\dfrac{5}{9}+\dfrac{3}{7}-\dfrac{1}{5}\\ =\left(\dfrac{1}{5}-\dfrac{1}{5}\right)+\left(-\dfrac{3}{7}+\dfrac{3}{7}\right)+\left(\dfrac{5}{9}-\dfrac{5}{9}\right)+\left(-\dfrac{2}{11}+\dfrac{2}{11}\right)+\left(\dfrac{7}{13}-\dfrac{7}{13}\right)+\left(-\dfrac{9}{16}\right)\\ =0+0+0+0+0+\dfrac{-9}{16}\\ =\dfrac{-9}{16}=-0,5625\)