a/b là phân số nha

\(\left(\frac{7}{20}+\frac{11}{15}-\frac{15}{12}\right):\left(\frac{11}{20}-\frac{26}{45}\right)\)

\(=\left(\frac{21}{60}+\frac{44}{60}-\frac{75}{60}\right):\left(\frac{99}{180}-\frac{104}{180}\right)\)

\(=-\frac{1}{6}:\frac{-1}{36}\)

\(=\frac{-36}{-6}\)

\(=6\)

( 7/20 + 11/15 - 15/12 ) : ( 11/20 - 26/45 ) 

= ( 21/60 + 44/60 - 75/60 ) : ( 99/180 - 104/180 ) 

= -1/6 : -1/36 

= -1/6 x (-36)

= 6

học tốt#

\(A=\left(\dfrac{5}{12}.\dfrac{21}{15}\right):\dfrac{1}{4}\)

\(=\dfrac{7}{12}:\dfrac{1}{4}\)

\(=\dfrac{28}{12}=\dfrac{7}{3}\)

\(B=\left(\dfrac{2}{7}:\dfrac{5}{4}\right).\left(\dfrac{5}{8}:2\right)\)

\(=\dfrac{8}{35}.\left(\dfrac{5}{8}:2\right)\)

\(=\dfrac{8}{35}.\dfrac{5}{16}\)

\(=\dfrac{1}{14}\)

\(C=\left(\dfrac{11}{15}.\dfrac{35}{44}\right).\left(\dfrac{1}{7}.\dfrac{4}{13}\right)\)

\(=\dfrac{7}{12}.\left(\dfrac{1}{7}.\dfrac{4}{13}\right)\)

\(=\dfrac{7}{12}.\left(\dfrac{1}{7}.\dfrac{4}{13}\right)\)

\(=\dfrac{7}{12}.\dfrac{4}{91}\)

\(=\dfrac{1}{39}\)

\(D=\left(\dfrac{7}{20}+\dfrac{11}{15}-\dfrac{15}{12}\right):\left(\dfrac{11}{20}-\dfrac{26}{45}\right)\)

\(=\left(\dfrac{13}{12}-\dfrac{15}{12}\right):\left(\dfrac{11}{20}-\dfrac{26}{45}\right)\)

\(=\dfrac{-1}{6}:\left(\dfrac{11}{20}-\dfrac{26}{45}\right)\)

\(=\dfrac{-1}{6}:\dfrac{-1}{36}\)

\(=6\)

bằng 6 nha

Lời giải:
$1+2+3+....+25$

$=(1+25)+(2+24)+(3+23)+(4+22)+(5+21)+(6+20)+(7+19)+(8+18)+(9+17)+(10+16)+(11+15)+(12+14)+13$

$=\underbrace{26+26+26+...+26}_{12}+13$

$=26\times 12+13=325$

\(a,\left(\dfrac{7}{20}+\dfrac{11}{15}-\dfrac{15}{12}\right):\left(\dfrac{11}{20}-\dfrac{26}{45}\right).\)

\(=\left(\dfrac{21}{60}+\dfrac{44}{60}-\dfrac{75}{60}\right):\left(\dfrac{99}{180}-\dfrac{104}{180}\right).\)

\(=\left(\dfrac{65}{60}-\dfrac{75}{60}\right):\left(-\dfrac{5}{180}\right).\)

\(=-\dfrac{10}{60}:\left(-\dfrac{5}{180}\right).\)

\(=-\dfrac{1}{6}:\left(-\dfrac{1}{36}\right).\)

\(=-\dfrac{1}{6}.\left(-36\right).\)

\(=\dfrac{-1.\left(-36\right)}{6}=\dfrac{36}{6}=6.\)

Vậy......

\(b,\dfrac{5-\dfrac{5}{3}+\dfrac{5}{9}-\dfrac{5}{27}}{8-\dfrac{8}{3}+\dfrac{8}{9}-\dfrac{8}{27}}:\dfrac{15-\dfrac{15}{11}+\dfrac{15}{121}}{16-\dfrac{16}{11}+\dfrac{16}{121}}.\)

\(=\dfrac{5\left(1-\dfrac{1}{3}+\dfrac{1}{9}-\dfrac{1}{27}\right)}{8\left(1-\dfrac{1}{3}+\dfrac{1}{9}-\dfrac{1}{27}\right)}:\dfrac{15\left(1-\dfrac{1}{11}+\dfrac{1}{121}\right)}{16\left(1-\dfrac{1}{11}+\dfrac{1}{121}\right)}.\)

\(=\dfrac{5}{8}:\dfrac{15}{16}.\)

\(=\dfrac{5}{8}.\dfrac{16}{15}=\dfrac{5.16}{8.15}=\dfrac{1.2}{1.3}=\dfrac{2}{3}.\)

Vậy......

c, (làm tương tự câu b).

~ Học tốt!!! ~