15X14-1/13X15+14=15X13+15-1/13X15+14

=15X13+14/13X15+14

=1

k đúng cho mk nha

1 nhé bạn

bạn có thể cho mình các bước giải bài này được không??

a, \(\dfrac{15\times14-1}{13\times15+14}\)

 = \(\dfrac{15\times\left(13+1\right)-1}{13\times15+14}\) 

= \(\dfrac{13\times15+15-1}{13\times15+14}\) 

= \(\dfrac{13\times15+14}{13\times15+14}\)

= 1

c, \(\dfrac{1+2+3+4+5+6+7+8+9}{10}\)

= \(\dfrac{\left(9+1\right)\times\left\{\left(9-1\right):1+1\right\}:2}{10}\)

= \(\dfrac{10\times9:2}{10}\)

= \(\dfrac{9}{2}\)

\(A=13.15+15.17+17.19+...+99.101\)

\(\Rightarrow6A=13.15.6+15.17.6+17.19.6+...+99.101.6\)

\(\Rightarrow6A=13.15.\left(17-11\right)+15.17.\left(19-13\right)+17.19.\left(21-15\right)+...+99.101.\left(103-97\right)\)

\(\Rightarrow6A=\left(13.15.17-11.13.15\right)+\left(15.17.19-13.15.17\right)+\left(17.19.21-15.17.19\right)+...+\left(99.101.103-97.99.101\right)\)

\(\Rightarrow6A=99.101.103-11.13.15\)

\(\Rightarrow6A=1027752\)

\(\Rightarrow A=171292\)

\(\dfrac{3}{7}.\dfrac{11}{13}-\dfrac{3}{13}.\dfrac{15}{7}.\dfrac{-17}{7}\)

= \(\dfrac{33}{91}-\dfrac{-765}{673}\)

= 1,4993387

=1/11 - 1/13 + 1/13 - 1/15 +...+1/19 - 1/21

=1/11-1/21=10/231

2/11x13+2/13x15+2/15x17+...+2/97x99

=1/11-1/13+1/13-1/15+1/15-1/17+...+1/97-1/99

=1/11-1/99

=8/99

thank you 

= 2/11.13 + 2/13.15 + ... + 2/97.99

= 2/11 .2/13 + 2/13 . 2/15 + ... + 2/97 . 2/97

= 2/11 + 2/97

= ......tu tinh

6.712565785

6.712565785

chắc cgắn 10000%

6,712565785