Question

Tính nhanh

a) 1/3. -4/5+ 1/3. -6/5

b) 3/7. 9/25- 1/14. 1/13

Answer 1

Giải:

a) \(\dfrac{1}{3}.\left(-\dfrac{4}{5}\right)+\dfrac{1}{3}.\left(-\dfrac{6}{5}\right)\)

\(=\dfrac{1}{3}\left[-\dfrac{4}{5}+\left(-\dfrac{6}{5}\right)\right]\)

\(=\dfrac{1}{3}\left[-\dfrac{4}{5}-\dfrac{6}{5}\right]\)

\(=\dfrac{1}{3}\left(-\dfrac{10}{5}\right)\)

\(=\dfrac{-10}{15}=-\dfrac{2}{3}\)

Vậy ...

b) \(\dfrac{3}{7}.\dfrac{9}{25}-\dfrac{1}{14}.\dfrac{1}{13}\)

\(=\dfrac{1}{7}.\dfrac{27}{25}-\dfrac{1}{7}.\dfrac{1}{26}\)

\(=\dfrac{1}{7}\left(\dfrac{27}{25}-\dfrac{1}{26}\right)\)

\(=\dfrac{1}{7}.\dfrac{677}{650}\)

\(=\dfrac{677}{4550}\)

Vậy ...