`(12/26+5/8)+7/13`

`=(6/13+5/8)+7/13`

`=(6/13+7/13)+5/8`

`=1+5/8=13/8`

`(12/26 +5/8) +7/13 `

`= 6/13 + 5/8 + 7/13`

`= (6/13 + 7/13) + 5/8`

`= 13/13 + 5/8`

`= 1 + 5/8 `

`= 8/8 + 5/8 `

`= 13/8`

(12/26+5/8)+7/13

=(12/26+7/13)+5/8

=1+5/8=8/8+5/8=13/8

6/13 + 5/8 + 7/13

= 6/13 + 7/13 + 5/8

= 1 + 5/8 = 1/5/8 

=6/13+7/13+5/8=1+5/8=13/8

\(\dfrac{12}{13}+\dfrac{2}{7}+\dfrac{8}{13}+\dfrac{6}{13}+\dfrac{5}{7}\)
\(=\left(\dfrac{12}{13}+\dfrac{8}{13}+\dfrac{6}{13}\right)+\left(\dfrac{2}{7}+\dfrac{5}{7}\right)\)
\(=2+1\)
\(=3\)

= ( 12/13 + 8/13 + 6/13 ) + ( 2/7 + 5/7 )

= 26/13 + 7/7

= 2 + 1

= 3

12/13 + 2/7 + 8/13 + 6/13 + 5/7

= ( 2/7 + 5/7 ) + ( 12/13 + 8/13 + 6/13 )

= 1 + 2

= 3

=(12/13+8/13+6/13)+(2/7+5/7)=2+1=3

8/27+4/5+19/27+11/15=(8/27+19/27) + (4/5+11/15)

                                    = 1+ (12/15+11/15)

                                    = 1+ 1/8/15=2/8/15

12/13+2/7+8/13+6/13+5/7=(12/13+8/13+6/13) + (2/7+5/7)

                                         = 2+ 1

                                         =3

Ý a có thể bạn chép nhầm 4/5 rồi

= 2 + 1=3 nhé bạn

câu a) lấy mẫu số chung cộng với nhau

câu b) lấy 1 để ngoài nhân r 1/2-1/3 rồi tương tự

12/13-2/7-8/13+6/13-5/7=1

\(\frac{12}{13}-\frac{2}{7}+\frac{8}{13}+\frac{6}{13}-\frac{5}{7}\)

\(=\left(\frac{12}{13}+\frac{8}{13}+\frac{6}{13}\right)-\left(\frac{2}{7}+\frac{5}{7}\right)\)

\(=\frac{26}{13}-\frac{7}{7}\)

\(=2-1\)

\(=1\)