b,\(\Rightarrow\)\(\left(\frac{1}{3}+\frac{1}{6}+\frac{1}{10}+...+\frac{2}{x\left(x+1\right)}\right):2=\frac{2013}{2015}:2\)

\(\Rightarrow\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+...+\frac{1}{x\left(x+1\right)}=\frac{2013}{4030}\)

\(\Rightarrow\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+...+\frac{1}{x.\left(x+1\right)}=\frac{2013}{4030}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+...+\frac{1}{x}-\frac{1}{x+1}=\frac{2013}{4030}\)

\(\Rightarrow\frac{1}{2}-\frac{1}{x+1}=\frac{2013}{4030}\)

\(\Rightarrow\frac{1}{x+1}=\frac{1}{2015}\)

\(\Rightarrow\)\(x+1=2015\)

\(\Rightarrow x=2014\)

a, 2/3x -3/2.x-1/2x=5/12

    x.(2/3-3/2-1/2)=5/12

                 x. -4/3=5/12

                          x=5/12:-4/3

                          x=-5/16

b,2/6+2/12+2/20+...+2/x.(x+1)=2013/2015

   2/2.3+2/3.4+2/4.5+...+2/x.(x+1)=2013/2015

   1/2(1-1/3+1/3-1/4+1/4-1/5+...+1/x-1/x+1)=2013/2015

                                                1/2(1-1/x+1)=2013/2015

                                                 1-1/x+1=2013/2015 : 1/2

                                                  1-1/x+1=4206/2015

                                                      suy ra đề sai

Ta có : \(D=\frac{1598}{66}\)

\(E=\frac{5656}{55}\)

E=(-0,17+3+5/9-2-36/97).(1/12-1/12)=(-0,17+3+5/9-2-36/97).0=0

Bạn học phá ngoặc đổi dấu chưa nhỉ?

5/9 - ( 3/5 - 4/9 ) + 3/5

= 5/9 - 3/5 + 4/9 + 3/5

= 5/9 + 4/9

= 9/9 = 1

kết quả bằng 1

a/=\(27\frac{51}{59}-7\frac{51}{59}+\frac{1}{3}\)

=20+\(\frac{1}{3}\)

=\(\frac{61}{3}\)

qwertyuiopasdfgggggghjkllzxcvbnmm,.//234567890-=`

\(a)\frac{\left(\frac{3}{10}-\frac{4}{15}-\frac{7}{20}\right).\frac{5}{19}}{\left(\frac{1}{14}+\frac{1}{7}-\frac{-3}{35}\right).\frac{-4}{3}}\)\(=\frac{\frac{-19}{60}.\frac{5}{19}}{\frac{3}{10}.\frac{-4}{3}}=\frac{5}{24}\)

Hok tốt

Yume Nguyễn bạn giải giúp mk phần b đc k

a)\(11\frac{1}{4}-\left(2\frac{5}{7}+5\frac{1}{4}\right)\)

\(=\frac{45}{4}-\left(\frac{19}{7}+\frac{21}{4}\right)\)

\(=\frac{45}{4}-\left(\frac{76}{28}+\frac{147}{28}\right)\)

\(=\frac{45}{4}-\frac{223}{28}\)

\(=\frac{315}{28}-\frac{223}{28}\)

\(=\frac{23}{7}\)

b) \(\left(8\frac{5}{11}+3\frac{5}{8}\right)-3\frac{5}{11}\)

   \(=\left(\frac{93}{11}+\frac{29}{8}\right)-\frac{38}{11}\)

   \(=\left(\frac{744}{88}+\frac{319}{88}\right)-\frac{38}{11}\)

   \(=\frac{1063}{88}-\frac{38}{11}=\frac{1063}{88}-\frac{304}{88}\)

    \(=\frac{69}{8}\)

1a) \(11\frac{1}{4}-\left(2\frac{5}{7}+5\frac{1}{4}\right)\)

\(=11\frac{1}{4}-2\frac{5}{7}-5\frac{1}{4}\)

\(=11\frac{1}{4}-5\frac{1}{4}-2\frac{5}{7}\)

\(=6-2\frac{5}{7}=3\frac{2}{7}=\frac{23}{7}\)

2a) \(x\div8,25=\left(-2,2\right)\)

\(\Leftrightarrow x=-18,15\)