= 4x4/3x7+ 4x4/7x11+ 4x4/11x15 = 4x(4/3x7 + 4/7x11+4/11x15) =4x(1/3-1/7+1/7-1/11+1/11-1/15) =4x(1/3-1/15)=4x4/15= 16/15.

\(\dfrac{8}{7}+\dfrac{-6}{7}.\dfrac{4}{11}-\dfrac{4}{11}.\dfrac{5}{11}\)

\(=\dfrac{8}{7}+\dfrac{4}{11}\left(-\dfrac{6}{7}-\dfrac{5}{11}\right)\)

\(=\dfrac{8}{7}+\dfrac{4}{11}.\dfrac{-101}{77}\)

\(=\dfrac{8}{7}+-\dfrac{404}{847}\)

\(=\dfrac{564}{847}\)

Sửa đề:

\(\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+...+\frac{28}{1995}\)

\(=\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+...+\frac{4}{285}\)

\(=\frac{4}{3.7}+\frac{4}{7.11}+\frac{4}{11.15}+\frac{4}{15.19}\)

\(=\frac{1}{3}-\frac{1}{7}+\frac{1}{7}-\frac{1}{11}+\frac{1}{11}-\frac{1}{15}+\frac{1}{15}-\frac{1}{19}\)

\(=\frac{1}{3}-\frac{1}{19}\)

\(=\frac{16}{57}\)

hình như @@Kamado Tajnirou @@ bạn làm sai rồi

a, \(\dfrac{38}{7}\) + ( \(\dfrac{16}{7}\) - \(\dfrac{5}{3}\))

= \(\dfrac{38}{7}\) + \(\dfrac{16}{7}\) - \(\dfrac{5}{3}\)

= \(\dfrac{54}{7}\) - \(\dfrac{5}{3}\)

= \(\dfrac{162}{21}\) - \(\dfrac{35}{21}\)

= \(\dfrac{127}{21}\)

b, \(\dfrac{29}{9}\) - ( \(\dfrac{14}{9}\) + \(\dfrac{11}{9}\) )

= \(\dfrac{29-14-11}{9}\)

= \(\dfrac{4}{9}\)

c, ( \(\dfrac{2}{7}\) + \(\dfrac{3}{8}\) + \(\dfrac{12}{7}\) + \(\dfrac{5}{8}\) ) - \(\dfrac{19}{63}\)

= ( \(\dfrac{2+12}{7}\) + \(\dfrac{3+5}{8}\)) - \(\dfrac{19}{63}\)

= \(\left(1+2\right)\) - \(\dfrac{19}{63}\)

= \(3-\dfrac{19}{63}\)

= \(\dfrac{189}{63}\) - \(\dfrac{19}{63}\)

= \(\dfrac{170}{63}\)

d, \(\dfrac{3}{7}\) . \(\dfrac{4}{9}\) + \(\dfrac{4}{9}\) . \(\dfrac{4}{7}\) - \(\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) . ( \(\dfrac{3}{7}\) + \(\dfrac{3}{7}\) ) - \(\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) . \(1-\dfrac{4}{9}\)

= \(\dfrac{4}{9}\) - \(\dfrac{4}{9}\)

= 0

chú ý dấu chấm là dấu nhân

mik tick cho

3/11 x 2 = 6/11

6/11 : 3/11 = 2

6/11 : 2 = 3/11

2/3 x 11 = 22/3

4/2 x 7 = 14

8/7 : 2/7 = 4

8/7 : 4 = 2/7

2/7 x 4 = 8/7

(4+11):15+(35+64):99+(2+5):7=15:15+99:99+7:7=1+1+1=3

`4/15+35/99+11/15-2/7+64/99-5/7`

`=(4/15+11/15)+(35/99+64/99)-(2/7+5/7)`

`=15/15+99/99-7/7`

`=1+1-1`

`=2-1`

`=1`

1

\(\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{-2}{11}+\dfrac{4}{-9}+\dfrac{7}{15}\)

=\(\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)-\dfrac{2}{11}\)

=\(-1+1-\dfrac{2}{11}=\dfrac{-2}{11}\)

\(=\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)+\dfrac{-2}{11}\\ =-1+1+\dfrac{-2}{11}\\ =0+\dfrac{-2}{11}=\dfrac{-2}{11}\)

\(\dfrac{-5}{9}+\dfrac{8}{15}+\dfrac{-2}{11}+\dfrac{4}{-9}+\dfrac{7}{15}\)

\(=\left(\dfrac{-5}{9}+\dfrac{-4}{9}\right)+\left(\dfrac{8}{15}+\dfrac{7}{15}\right)+\dfrac{-2}{11}\)

\(=\dfrac{-9}{9}+\dfrac{15}{15}+\dfrac{-2}{11}\)

\(=\left(-1\right)+1-\dfrac{-2}{11}\)

\(=0+\dfrac{-2}{11}\)

\(=\) \(\dfrac{-2}{11}\)