Question

tính bằng cách thuận tiện
4/7 x 5/6 + 3/7 x 5/6
7/9 x 8/5 - 7/9 x 3/5
2006/2005 x 3/4 - 3/4 x 1/2005
 

Answer 1

\(a,=\dfrac{5}{6}\left(\dfrac{4}{7}+\dfrac{3}{7}\right)\\ =\dfrac{5}{6}.\dfrac{7}{7}=\dfrac{5}{6}.1=\dfrac{5}{6}\\ b,=\dfrac{7}{9}.\left(\dfrac{8}{5}-\dfrac{3}{5}\right)\\ =\dfrac{7}{9}.\dfrac{5}{5}\\ =\dfrac{7}{9}.1=\dfrac{7}{9}\\ c,=\dfrac{3}{4}.\left(\dfrac{2006}{2005}-\dfrac{1}{2005}\right)\\ =\dfrac{3}{4}.1=\dfrac{3}{4}\)

Answer 2

`(4)/(7)xx(5)/(6)+(3)/(7)xx(5)/(6)`

`=(5)/(6)xx((4)/(7)+(3)/(7))`

`=(5)/(6)xx(7)/(7)`

`=(5)/(6)xx1=5/6`

``

`(7)/(9)xx(8)/(5)-(7)/(9)xx(3)/(5)`

`=(7)/(9)xx((8)/(5)-(3)/(5))`

`=(7)/(9)xx(5)/(5)`

`=(7)/(9)xx1=7/9`

``

`(2006)/(2005)xx(3)/(4)-(3)/(4)xx(1)/(2005)`

`=(3)/(4)xx((2006)/(2005)-(1)/(2005))`

`=(3)/(4)x(2005)/(2005)`

`=(3)/(4)x1=3/4`