Question

[Huynh Chau Anh Kha]

7/13.7/15 -5/12.21/39+49/91.8/15

Answer 1

[Phạm Minh Châu]

\(\dfrac{7}{13}.\dfrac{7}{15}-\dfrac{5}{12}.\dfrac{21}{39}+\dfrac{49}{91}.\dfrac{8}{15}\)

= \(\dfrac{7}{13}.\dfrac{7}{15}-\dfrac{5}{12}.\dfrac{7}{13}+\dfrac{7}{13}.\dfrac{8}{15}\)

= \(\dfrac{7}{13}.\left(\dfrac{7}{15}-\dfrac{5}{12}+\dfrac{8}{15}\right)\)

= \(\dfrac{7}{13}.\left(\dfrac{7}{15}+\dfrac{8}{15}-\dfrac{5}{12}\right)\)

= \(\dfrac{7}{13}.\left(1-\dfrac{5}{12}\right)\)

= \(\dfrac{7}{13}.\dfrac{7}{12}=\dfrac{49}{156}\)