Question

tính nhanh 2 phần 3 + (5 phần 7 + âm 2 phần 3)

Answer 1

\(=\dfrac{2}{3}+\left(\dfrac{5}{7}+\dfrac{-2}{3}\right)=\left[\dfrac{2}{3}+\dfrac{-2}{3}\right]+\dfrac{5}{7}\\ =0+\dfrac{5}{7}=\dfrac{5}{7}\)

Answer 2

\(\dfrac{2}{3}+\left(\dfrac{5}{7}+\dfrac{-2}{3}\right)=\dfrac{2}{3}+\dfrac{5}{7}+\dfrac{-2}{3}=\left(\dfrac{2}{3}+\dfrac{-2}{3}\right)+\dfrac{5}{7}=0+\dfrac{5}{7}=\dfrac{5}{7}\)

Answer 3

\(\dfrac{5}{7}\) chăng