Question

toán thức hiện dãy tính ( t ính nhanh n ếu có t hể  ) -3/5 +7/21 +-4/5 +7/5

 

Answer 1

   -3/5+7/21+-4/5+7/5
=(-3/5+-4/5+7/5)+7/21
=0+7/21
=7/21=1/3

Answer 2

\(-\dfrac{3}{5}+\dfrac{7}{21}+\dfrac{-4}{5}+\dfrac{7}{5}\)

= \((-\dfrac{3}{5}-\dfrac{4}{5}+\dfrac{7}{5})+\dfrac{7}{21}\)

= \(\dfrac{7}{21}=\dfrac{1}{3}\)

Answer 3

\(-\dfrac{3}{5}+\dfrac{7}{21}+\left(-\dfrac{4}{5}\right)+\dfrac{7}{5}\)

\(=\left[-\dfrac{3}{5}+\left(-\dfrac{4}{5}\right)+\dfrac{7}{5}\right]+\dfrac{7}{21}\)

\(=0+\dfrac{7}{21}=\dfrac{7}{21}\)

Answer 4

Ta có: \(\dfrac{-3}{5}+\dfrac{7}{21}+\dfrac{-4}{5}+\dfrac{7}{5}\)

\(=\left(-\dfrac{3}{5}-\dfrac{4}{5}+\dfrac{7}{5}\right)+\dfrac{1}{3}\)

\(=\dfrac{1}{3}\)

Answer 5

\(\dfrac{-3}{5}+\dfrac{7}{21}+\dfrac{-4}{5}+\dfrac{7}{5}\) 

\(=\left(\dfrac{-3}{5}+\dfrac{-4}{5}+\dfrac{7}{5}\right)+\dfrac{1}{3}\) 

\(=0+\dfrac{1}{3}\)  

\(=\dfrac{1}{3}\)