a) Ta có: BCNN(15,10) = 30 nên ta chọn mẫu số chung là 30

\(\frac{11}{15}+\frac{9}{10}=\frac{22}{30}+\frac{27}{30}=\frac{49}{30}\)

b) Ta có: BCNN(6,9,12) = 36 nên ta chọn mẫu số chung là 36

\(\frac{5}{6} + \frac{7}{9} + \frac{{11}}{{12}} = \frac{{30}}{{36}} + \frac{{28}}{{36}} + \frac{{33}}{{36}} = \frac{{91}}{{36}}\)

c) Ta có: BCNN(24,21) = 168 nên ta chọn mẫu số chung là 168

\(\frac{7}{{24}} - \frac{2}{{21}} = \frac{{49}}{{168}} - \frac{{16}}{{168}} = \frac{{33}}{{168}}=\frac{11}{56}\)

d) Ta có: BCNN(36,24) = 72 nên ta chọn mẫu số chung là 72

\(\frac{{11}}{{36}} - \frac{7}{{24}} = \frac{{22}}{{72}} - \frac{{21}}{{72}} = \frac{1}{{72}}\)

dài quá! mình bó tay luôn!

\(\frac{5}{9}:\left(\frac{1}{11}-\frac{5}{22}\right)+\frac{5}{9}:\left(\frac{1}{15}-\frac{2}{3}\right)\)

\(=\frac{5}{9}:\left(\frac{-3}{22}\right)+\frac{5}{9}:\left(\frac{-3}{5}\right)\)

\(=\frac{5}{9}.\left(-\frac{22}{3}\right)+\frac{5}{9}.\left(-\frac{5}{3}\right)\)

\(=\frac{5}{9}.\left[-\frac{22}{3}+\left(-\frac{5}{3}\right)\right]\)

\(=\frac{5}{9}.\left(-9\right)\)

\(=-5\)

\(\frac{5}{9}:\left(\frac{1}{11}-\frac{5}{22}\right)+\frac{5}{9}:\left(\frac{1}{15}-\frac{2}{3}\right)\)

\(=\frac{5}{9}:\left[\left(\frac{1}{11}-\frac{5}{22}\right)+\left(\frac{1}{15}-\frac{2}{3}\right)\right]\)

\(=\frac{5}{9}:\left[-\frac{3}{22}-\frac{3}{5}\right]\)

\(=\frac{5}{9}:\frac{-81}{110}=\frac{5}{9}.\frac{-110}{81}\)

\(=-\frac{550}{729}\)

\(\frac{\frac{1}{9}-\frac{1}{7}-\frac{1}{11}}{\frac{4}{9}-\frac{4}{7}-\frac{4}{11}}+\frac{\frac{3}{5}-\frac{3}{25}-\frac{3}{125}-\frac{3}{625}}{\frac{4}{5}-\frac{4}{25}-\frac{4}{125}-\frac{4}{625}}\)

\(=\frac{\frac{1}{9}-\frac{1}{7}-\frac{1}{11}}{4\left(\frac{1}{9}-\frac{1}{7}-\frac{1}{11}\right)}+\frac{3\left(\frac{1}{5}-\frac{1}{25}-\frac{1}{125}-\frac{1}{625}\right)}{4\left(\frac{1}{5}-\frac{1}{25}-\frac{1}{125}-\frac{1}{625}\right)}\)

\(=\frac{1}{4}+\frac{3}{4}=\frac{4}{4}=1\)

5/15+14/25-12/9+2/7+11/25=(5/15+2/7)+(14/25+11/25)-12/9=17/35+1-12/9=16/105

=\(\left(\frac{5}{15}-\frac{12}{9}\right)+\left(\frac{14}{25}+\frac{11}{15}\right)+\frac{2}{7}\)

=\(\left(\frac{1}{3}-\frac{4}{3}\right)+1+\frac{2}{7}\)

=\(\frac{-3}{3}+1+\frac{2}{7}=-1+1+\frac{2}{7}\)

=\(\frac{2}{7}\)

M=3/1.2-5/2.3+7/3.4-9/4.5+11/5.6-13/6.7+15/7.8+17/8.9

   =(1/1.1+2/1.2)-(2/2.3+3/2.3)+(3/3.4+4/3.4)-(4/4.5+5/4.5)+...+(8/8.9+9/8.9)(phần ... là làm tương tự nhé)

   =1/2+1-(1/3+1/2)+(1/4+1/3)-(1/5+1/4)+...+(1/9+1/8)(phần ... là làm tương tự nhé)

   =1+(1/2-1/2)+(1/3-1/3)+(1/4-1/4)+...+(1/8-1/8)-1/9

   =1+0+0+0+...+0-1/9

   =1-1/9

   =8/9

\(C=\frac{\left(-3\right)^{10}.15^5}{25^3.\left(-9\right)^7}\)

    \(=\frac{\left(-3\right)^{10}.\left(3.5\right)^5}{\left(5.5\right)^3.\left(-3.3\right)^7}\)

     \(=\frac{\left(-3\right)^{10}.3^5.5^5}{5^3.5^3.\left(-3\right)^7.3^7}\)

      \(=\frac{\left(-3\right)^3.1.5^2}{5^3.1.1.3^2}\)

      \(=\frac{\left(-3\right).1.1}{5.1.1.1}\)

       \(=-\frac{3}{5}\)

1.c,

\(\frac{\left(-3\right)^{10}.15^5}{25^3.\left(-9\right)^7}=\frac{3^{10}.\left(3.5\right)^5}{\left(5^2\right)^3.-\left(3^2\right)^7}\)\(=\frac{3^{10}.3^5.5^5}{5^6.-3^{14}}=\frac{3^{15}.5^5}{5^6.-3^{14}}\)\(=\frac{3.1}{5.-1}\)\(=\frac{3}{-5}=\frac{-3}{5}\)

chúc bn học tốt!

\(\frac{-3}{11}:\frac{17}{15}+\frac{-3}{11}:\frac{17}{2}+\frac{8}{11}\)

\(=\frac{-3}{11}.\frac{15}{17}+\frac{-3}{11}.\frac{2}{17}+\frac{8}{11}\)

\(=\frac{-3}{11}.\left(\frac{15}{17}+\frac{2}{17}\right)+\frac{8}{11}\)

\(=\frac{-3}{11}.1+\frac{8}{11}\)

\(=\frac{-3}{11}+\frac{8}{11}\Rightarrow\frac{5}{11}\)

K mik nhe

\(\frac{-3}{11}:\frac{17}{15}+\frac{-3}{11}:\frac{17}{2}+\frac{8}{11}\)

\(=\frac{-3}{11}.\left(\frac{15}{17}+\frac{2}{17}\right)+\frac{8}{11}\)

\(=\frac{-3}{11}.1+\frac{8}{11}\)

=\(\frac{-3}{11}+\frac{8}{11}\)

\(=\frac{5}{11}\)

\(M=\frac{1}{16}\)

M= 9/40-11/60+13/84-15/112

M=378/1680-308/1680+260/1680-225/1680

M=\(\frac{378-308+260-225}{1680}\)

M=\(\frac{105}{1680}\)

M= \(\frac{1}{16}\)