nhiều thế

sfdhg 

\(\frac{19}{15}+\frac{31}{23}-\frac{4}{15}-\frac{8}{23}=\frac{19-4}{15}+\frac{31-8}{23}=\frac{15}{15}+\frac{23}{23}=1+1=2\)

\(\frac{19}{15}+\frac{31}{23}-\frac{4}{15}-\frac{8}{23}\)

\(=\frac{19-4}{15}+\frac{31-8}{23}\)

\(=\frac{15}{15}+\frac{23}{23}\)

\(=1+1=2\)

\(\frac{19}{15}+\frac{31}{23}-\frac{4}{15}-\frac{8}{23}\)

\(=\left(\frac{19}{15}-\frac{4}{15}\right)+\left(\frac{31}{23}-\frac{8}{23}\right)\)

\(=\frac{15}{15}+\frac{23}{23}\)

\(=1+1=2\)

\(\frac{19}{15}+\frac{31}{23}-\frac{14}{15}-\frac{8}{23}\)

\(=\frac{19}{15}-\frac{4}{15}+\frac{31}{23}-\frac{8}{23}\)

\(=1+1=2\)

chúc bạn học giỏi

19 / 15 + 31 / 25 - 4 / 15 - 8 / 23

= ( 19 / 15 - 4 / 15 ) + ( 31 / 23 - 8 / 23 )

= 15 / 15 + 23 / 23

= 1 + 1 = 2

7/18+11/18+4/23+19/23=1+1=2

1+2+3+4+5+6+7+8+9+10+11+12+13+14+15+16+17+18+19+20

=(1+19)+(2+18)+(3+17)+(4+16)+(5+15)+(6+14)+(7+13)+(8+12)+(9+11)+20+10

=20+20+20+20+20+20+20+20+20+20+10

=20×10+10

=200+10

=210

= ( 1 + 19 ) + ( 2 + 18 ) + ( 3 + 17 ) + (4 + 16 ) + ( 5 + 15 ) + ( 6 + 14 ) + ( 7 + 13 ) + ( 8 + 12) + ( 9+ 11 ) + 20

= 20 + 20 + 20 +20 +  20 +20 + 20 + 20 + 20 +20

= 20 x 10

= 200

tui đầu tiên đó 

Ta có : \(1+2+3+...+19+20\)

          \(=\frac{\left(20+1\right).20}{2}=\frac{21.20}{2}=210\)

lấy (7/18+11/18)+(4/23+19/23)=2

vì 7/18+11/18=18/18=1

   4/23+19/23=23/23=1

nên 1+1=2

Đ/s;2

=2

Vì 7 phần mười tám cộng 11 phần 18 bằng 1 và 4 phần 23 + 19 phần 23=1 nên 1+1=2

=(7/18+11/18)+(4/23+19/23)

=18/18+(4/23+19/23)

=1+23/23

=1+1

=2

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

Tách từng câu ra giùm, như này ai giải nổi:)))))