C

C

C NHA BẠN 

CHÚC BẠN HỌC TỐT ^^

13/19x23/11-13/19x8/11-13/19x4/11

=(23/11-8/11-4/11)=11/11=1

=13/19x1

=13/19

\(\frac{13}{19}\cdot\frac{23}{11}-\frac{13}{19}\cdot\frac{8}{11}-\frac{13}{19}\cdot\frac{4}{11}=\frac{13}{19}\cdot\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}\cdot1=\frac{13}{19}\)

Ta có:

3.7/19-7/13.5/19-7/19.8/13

=3.7/19-7/19.5/13-7/19.8/13

=3.7/19-7/19.(5/13+8/13)

=3.7/19-7/19.1

=7/19.(3-1)

=7/19.2

=14/19

Ta có:

3.7/19-7/13.5/13-7/19.8/13

=3.7/19-7/19.5/13-7/19.8/13

=3.7/19-7/19.(5/13+8/13)

=3.7/19-7/19.1

=7/19.(3-1)

=7/19.2

=14/19

13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11

= 13/19 x (23/11 - 8/11 - 4/11)

= 13/19 x 1

= 13/19

\(\dfrac{13}{19}\times\dfrac{23}{11}-\dfrac{13}{19}\times\dfrac{8}{11}-\dfrac{13}{19}\times\dfrac{4}{11}\\ =\dfrac{13}{19}\times\left(\dfrac{23}{11}-\dfrac{8}{11}-\dfrac{4}{11}\right)\\ =\dfrac{13}{19}\times1=\dfrac{13}{19}\)

câu b, 20/5x7 + 20/7x9 + 20/ 9 x11 + ..... 20 / 33 x35

\(\frac{13}{19}\times\frac{23}{11}-\frac{13}{19}\times\frac{8}{11}-\frac{13}{19}\times\frac{4}{11}\)

\(=\frac{13}{19}\times\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}\times1\)

\(=\frac{13}{19}\)

13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11

= 13/19 x (23/11 - 8/11 - 4/11)

= 13/19 x 1

= 13/19

\(\frac{13}{19}.\frac{23}{11}-\frac{13}{19}.\frac{8}{11}-\frac{13}{19}.\frac{4}{11}\)

\(=\frac{13}{19}.\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}.\frac{11}{11}\)

\(=\frac{13}{19}.1\)

\(=\frac{13}{19}\)

21.(19-13) - 19(21-13)

= 21.19 - 21.13 - 19.21 + 19.13

= ( 21.19 - 19.21) - 13.( 21 - 19)

= 0 - 13. 2

= - 26 

29.(19 - 13) - 19.(19 - 13)

= 29.6 - 19.6

= 6.(29 - 19)

= 6.10

= 60

29 . (19 - 13 ) - 19 . ( 29 - 13 )

=29 . 6 - 19 . 16

=174 - 304

=130

29․(19-13)-19․(29-13)

= 29․6-19․6

= 6․(29-19)

= 6․10

= 60