= 1/15 - 1/31 + 1/31 - 1/45 + 1/45 - 1/52 + 1/52 - 1/65 + 1/13.70

= 1/15 - 1/65 + 1/13.70

= 2/39 + 1/910

= 11/210

Tk mk nha

=(1/15-1/31+1/31-1/45+1/45-1/52+1/52-1/65)+1/910

​=(1/15-1/65)+1/910

​=2/39+1/910=140/2730+3/2730=11/210

​Tk mình nha bn !

​

37/663

giúp mk đi, mai mk nộp rùi đó

. Tham khảo nha !!! 

\(\frac{16}{15.31}+\frac{14}{31.45}+\frac{7}{45.52}+\frac{7}{52.65}+\frac{1}{13.70}\)

\(=\frac{16}{15.31}+\frac{14}{31.45}+\frac{7}{45.52}+\frac{7}{52.65}+\frac{5}{65.70}\)

\(=\frac{1}{15}-\frac{1}{31}+\frac{1}{31}-\frac{1}{45}+\frac{1}{45}-\frac{1}{52}+\frac{1}{52}-\frac{1}{65}+\frac{1}{65}-\frac{1}{70}\)

\(=\frac{1}{15}-\frac{1}{70}\)

\(=\frac{70}{1050}-\frac{15}{1050}\)

\(=\frac{55}{1050}\)

\(=\frac{11}{210}\)

Chúc bạn học tốt !!! 

Lời giải:

$A=\frac{15-5}{5.15}+\frac{31-15}{15.31}+\frac{45-31}{31.45}+\frac{52-45}{45.52}+\frac{65-52}{52.65}+\frac{1}{13.70}+\frac{1}{70.15}$

$=\frac{1}{5}-\frac{1}{15}+\frac{1}{15}-\frac{1}{31}+\frac{1}{31}-\frac{1}{45}+\frac{1}{45}-\frac{1}{52}+\frac{1}{52}-\frac{1}{65}+\frac{1}{70}(\frac{1}{13}+\frac{1}{15})$

$=\frac{1}{5}-\frac{1}{65}+\frac{1}{70}.\frac{28}{195}$

$=\frac{12}{65}+\frac{2}{95}$

$=\frac{254}{1325}$

\(A=\dfrac{5}{11}.\dfrac{5}{7}+\dfrac{5}{11}.\dfrac{2}{7}+\dfrac{6}{11}=\dfrac{5}{11}\left(\dfrac{5}{7}+\dfrac{2}{7}\right)+\dfrac{6}{11}=\dfrac{5}{11}.1+\dfrac{6}{11}=\dfrac{5}{11}+\dfrac{6}{11}=\dfrac{11}{11}=1\)

\(B=\dfrac{3}{13}.\dfrac{6}{11}+\dfrac{3}{13}.\dfrac{9}{11}-\dfrac{3}{13}.\dfrac{4}{11}=\dfrac{3}{13}\left(\dfrac{6}{11}+\dfrac{9}{11}-\dfrac{4}{11}\right)=\dfrac{3}{13}.1=\dfrac{3}{13}\)

\(C=\left(\dfrac{12}{16}-\dfrac{31}{22}+\dfrac{14}{91}\right)\left(\dfrac{1}{2}-\dfrac{1}{3}-\dfrac{1}{6}\right)=\left(\dfrac{12}{16}-\dfrac{31}{22}+\dfrac{14}{91}\right)\left(\dfrac{3}{6}-\dfrac{2}{6}-\dfrac{1}{6}\right)=\left(\dfrac{12}{16}-\dfrac{31}{22}+\dfrac{14}{91}\right).0=0\)

=( 19/13+7/13) + ( 17/9+1/9) + ( 7/3 + 2/3)

= 26/13 + 18/9 + 9/3

= 2 + 2+3

= 7

Lời giải:

$=(\frac{3}{5}+\frac{2}{5})+(\frac{5}{11}+\frac{16}{11})+(\frac{7}{13}+\frac{19}{13})$

$=\frac{5}{5}+\frac{22}{11}=\frac{26}{13}=1+2+2=5$