A= 7/8:(4/18-1/18)+7/8:(1/36-15/36)

=7/8:1/6+7/8:(-7/18)

=7/8:(1/6+-7/18)=7/8:(3/18+-7/18)=7/8:(-2/9)=-63/18=-7/2

còn ý b thì sao bạn??????

5và 3/8-1 và 5/6

a) 2/7+-3/8+11/7+1/3+1/7+5/-8

=(2/7+11/7+1/7)+(3/8+-5/8)+1/3

=2+2+1/3

=4+1/3

=13/3

b) -3/8+12/25+5/-8+2/-5+13/25

=(-3/8+-5/8)+(12/25+13/25)+-2/5

=-1+1+-2/5

=0+-2/5

=-2/5

c)7/8+1/8*3/8+1/8*5/8

=7/8+1/8*(3/8+5/8)

=7/8+1/8*1

=7/8+1/8

=1

a) 2/7+-3/8+11/7+1/3+1/7+5/-8

=(2/7+11/7+1/7)+(3/8+-5/8)+1/3

=2+2+1/3

=4+1/3

=13/3

b) -3/8+12/25+5/-8+2/-5+13/25

=(-3/8+-5/8)+(12/25+13/25)+-2/5

=-1+1+-2/5

=0+-2/5

=-2/5

c)7/8+1/8*3/8+1/8*5/8

=7/8+1/8*(3/8+5/8)

=7/8+1/8*1

=7/8+1/8

=1

bn ơi bài thái ngọc minh anh làm đúng còn cái bn trên đầu là chép của cậu ấy nha

a) 20,7 + 1,47 : 7 - 0,23 . 5

= 20,7 + 0,21 – 1,15

= 20,91 – 1,15

= 19,76

Ở trên vietjack có đó bn =)

a, 20,7 + 1,47 : 7 - 0,23 . 5

=\(\frac{207}{10}+\frac{147}{100}:7-\frac{23}{100}.5\)

= \(\frac{207}{10}+\frac{21}{100}-\frac{23}{20}\)

= \(\frac{2091}{100}+\frac{-23}{20}\)

= \(\frac{494}{25}\)

\(a,20,7+1,47:7-0,23\cdot5\)

\(=20,7+0,21-1,15=19,76\)

\(b,1\frac{4}{5}\cdot\frac{7}{8}+\frac{4}{29}:\frac{5}{58}-1\frac{3}{10}\)

\(=\frac{9}{5}\cdot\frac{7}{8}+\frac{4}{29}:\frac{5}{58}-\frac{13}{10}\)

\(=\frac{9\cdot7}{5\cdot8}+\frac{4}{29}\cdot\frac{58}{5}-\frac{13}{10}\)

\(=\frac{63}{40}+\frac{4}{1}\cdot\frac{2}{5}-\frac{13}{10}\)

\(=\frac{63}{40}+\frac{8}{5}-\frac{13}{10}=\frac{63}{40}+\frac{64}{40}-\frac{52}{40}=\frac{63+64-52}{40}=\frac{75}{40}=\frac{15}{8}\)

\(c)\) \(C=\frac{\frac{2}{7}+\frac{2}{5}+\frac{2}{17}-\frac{2}{293}}{\frac{3}{7}+\frac{3}{5}+\frac{3}{17}-\frac{3}{293}}\)

\(C=\frac{2\left(\frac{1}{7}+\frac{1}{5}+\frac{1}{17}-\frac{1}{293}\right)}{3\left(\frac{1}{7}+\frac{1}{5}+\frac{1}{17}-\frac{1}{193}\right)}\)

\(C=\frac{2}{3}\)

Bạn Cô nàng Thiên Bình làm đúng hết òi =.= 

a=7.[1/8+1/27-1/49]

   ------------------------

11.[1/8+1/27-1/49]

=7/11

cau b,c tuong tu nha h mk   

a)\(A=\frac{\frac{7}{8}+\frac{7}{27}-\frac{7}{49}}{\frac{11}{8}+\frac{11}{27}-\frac{11}{49}}\)

\(A=\frac{7.\left(\frac{1}{8}+\frac{1}{27}-\frac{1}{49}\right)}{11.\left(\frac{1}{8}+\frac{1}{27}-\frac{1}{49}\right)}\).

\(A=\frac{7}{11}\)

b)\(B=\frac{\frac{8}{9}-\frac{8}{27}-\frac{8}{81}+\frac{8}{243}}{4-\frac{4}{3}-\frac{4}{9}+\frac{4}{27}}\)

\(B=\frac{\frac{8}{9}.\left(1-\frac{1}{3}-\frac{1}{9}+\frac{1}{27}\right)}{4.\left(1-\frac{1}{3}-\frac{1}{9}+\frac{1}{27}\right)}\)

\(B=\frac{8}{9}:4=\frac{2}{9}\)

c)\(C=\frac{\frac{2}{7}+\frac{2}{5}+\frac{2}{17}-\frac{2}{293}}{\frac{3}{7}+\frac{3}{5}+\frac{3}{17}-\frac{3}{293}}\)\(C=\frac{2.\left(\frac{1}{7}+\frac{1}{5}+\frac{1}{17}-\frac{1}{239}\right)}{3.\left(\frac{1}{7}+\frac{1}{5}+\frac{1}{17}-\frac{1}{239}\right)}\)

C=\(\frac{2}{3}\)

\(\begin{array}{l}a)\left[ {{{\left( {\dfrac{3}{7}} \right)}^4}.{{\left( {\dfrac{3}{7}} \right)}^5}} \right]:{\left( {\dfrac{3}{7}} \right)^7}\\ = {\left( {\dfrac{3}{7}} \right)^{4 + 5}}:{\left( {\dfrac{3}{7}} \right)^7}\\ = {\left( {\dfrac{3}{7}} \right)^9}:{\left( {\dfrac{3}{7}} \right)^7}\\ = {\left( {\dfrac{3}{7}} \right)^{9-7}}\\= {\left( {\dfrac{3}{7}} \right)^2}\\b)\left[ {{{\left( {\dfrac{7}{8}} \right)}^5}:{{\left( {\dfrac{7}{8}} \right)}^4}} \right].\left( {\dfrac{7}{8}} \right)\\ = {\left( {\dfrac{7}{8}} \right)^{5 - 4}}.\left( {\dfrac{7}{8}} \right)\\ = \left( {\dfrac{7}{8}} \right).\left( {\dfrac{7}{8}} \right)\\ = {\left( {\dfrac{7}{8}} \right)^2}\\c)\left[ {{{\left( {0,6} \right)}^3}.{{\left( {0,6} \right)}^8}} \right]:\left[ {{{\left( {0,6} \right)}^7}.{{\left( {0,6} \right)}^2}} \right]\\ = {\left( {0,6} \right)^{3 + 8}}:{\left( {0,6} \right)^{7 + 2}}\\ = {\left( {0,6} \right)^{11}}:{\left( {0,6} \right)^9}\\ = {\left( {0,6} \right)^{11-9}}\\={\left( {0,6} \right)^2}.\end{array}\)

Đặt P = ... ( biểu thức đề bài ) 

Nhận xét: Với \(k\inℕ^∗\) ta có: 

\(\frac{k+2}{k!+\left(k+1\right)!+\left(k+2\right)!}=\frac{k+2}{k!+\left(k+1\right).k!+\left(k+2\right).k!}=\frac{k+2}{2.k!\left(k+2\right)}=\frac{1}{2.k!}\)

\(\Rightarrow\)\(P=\frac{1}{2.1!}+\frac{1}{2.2!}+...+\frac{1}{2.6!}=\frac{1}{2}\left(1+\frac{1}{2}+...+\frac{1}{720}\right)=...\)

b) \(\frac{5}{9}\)và \(\frac{5}{8}\) :Quy đồng mẫu số : \(\frac{5}{9}\) = \(\frac{5.8}{9.8}\) = \(\frac{40}{72}\) ; \(\frac{5}{8}\) = \(\frac{5.9}{8.9}\) = \(\frac{45}{72}\)

Vì \(\frac{40}{72}\) < \(\frac{45}{72}\) nên \(\frac{5}{9}\) < \(\frac{5}{8}\)

c)\(\frac{8}{7}\) và \(\frac{7}{8}\) :Quy đồng mẫu số: \(\frac{8}{7}\) = \(\frac{8.8}{7.8}\) = \(\frac{64}{56}\) ; \(\frac{7}{8}\) = \(\frac{7.7}{8.7}\) =\(\frac{49}{56}\)

Vì \(\frac{64}{56}\) > \(\frac{49}{56}\) nên \(\frac{8}{7}\) > \(\frac{7}{8}\)

bạn an đông à cái câu A của bạn sai một chút.

CHÚC BẠN HỌC TỐT !

a)\(\frac{3}{7}\) và\(\frac{2}{8}\) :Quy đồng mẫu số : \(\frac{3}{7}\) = \(\frac{3.8}{7.8}\) = \(\frac{24}{56}\) ; \(\frac{2}{8}\) = \(\frac{2.7}{8.7}\) = \(\frac{14}{56}\)

Vì \(\frac{24}{56}\) > \(\frac{14}{56}\) nên \(\frac{3}{7}\) > \(\frac{2}{8}\)

chim to vai lon