\(\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}=\frac{1}{1\times2}+\frac{1}{2\times3}+\frac{1}{3\times4}+\frac{1}{4\times5}+\frac{1}{5\times6}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}=1-\frac{1}{6}=\frac{5}{6}\)

 là hỗn số hả  bn ??

          \(A=11\frac{2}{1.3}+11\frac{2}{3.5}+11\frac{2}{5.7}+11\frac{2}{7.9}+11\frac{2}{9.11}\)

         \(A=11+\frac{2}{1.3}+11+\frac{2}{3.5}+11+\frac{2}{5.7}+11+\frac{2}{7.9}+11+\frac{2}{9.11}\)

         \(A=55+\frac{2}{1.3}+\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\)

        \(A=55+\frac{1}{1}-\frac{1}{3}+\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\)

       \(A=55+\frac{1}{1}-\frac{1}{11}\)

      \(A=56-\frac{1}{11}\)

     \(A=\frac{616}{11}-\frac{1}{11}=\frac{615}{11}\)

  Vậy A = 615 / 11 

Ax1/2=1/2+1/6+1/12+1/20+1/30+1/42

Ax1/2=1/1.2+1/2.3+1/3.4+...+1/6.7

Ax1/2=1-1/2+1/2-1/3+1/3-1/4+....+1/6-1/7

Ax1/2=1-1/7=6/7

=>A=6/7x2=12/7

A= \(\frac{1}{4}\)+ \(\frac{1}{12}\)+ \(\frac{1}{24}\)+ \(\frac{1}{40}\)+ \(\frac{1}{60}\)+ \(\frac{1}{84}\)
2A=\(\frac{1}{2}\)+ \(\frac{1}{6}\)+ \(\frac{1}{12}\)+\(\frac{1}{20}\)+ \(\frac{1}{30}\)+ \(\frac{1}{42}\)
2A=\(\frac{1}{1.2}\)+ \(\frac{1}{2.3}\)+ \(\frac{1}{3.4}\)+ \(\frac{1}{4.5}\)+ \(\frac{1}{5.6}\)+ \(\frac{1}{6.7}\)
2A=\(1-\frac{1}{2}\)\(+\frac{1}{2}\)\(-\frac{1}{3}\)\(+...+\)\(\frac{1}{6}\)\(-\frac{1}{7}\)
2A=\(1-\frac{1}{7}\)
2A=\(\frac{6}{7}\)
A=\(\frac{6}{7}:2\)
\(\Rightarrow A=\frac{3}{7}\)
Vậy \(A=\frac{3}{7}\)
Chúc bạn học tốt nhé!

\(=\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times\frac{4}{5}\times\frac{5}{6}\times\frac{6}{7}=\frac{1}{7}\)

a) Ta có: \(A=\frac{3535.232323}{353535.2323}=\frac{35.101.23.10101}{35.10101.23.101}=\frac{35}{23}\)

 \(B=\frac{3535}{3434}=\frac{35.101}{34.101}=\frac{35}{34}\)

\(C=\frac{2323}{2322}=\frac{2323}{2322}\)

Bài làm

a) 27x38+62x37-27x90

=27x38+62x(27+10)-27x90

=27x38+62x27+62x10-27x90

=27x(38+62-90)+620

=27x10+620

=270+620

=890

b)1994x867+1995x133

=1994x867+(1994+1)x133

=1994x867+1994x133+1x133

=1994x(867+133)+133

=1994x1000+133

=1994000+133

=1994133

Chúc học tốt!

a: 27x38+62x37-27x90

=62x37-27x(90-38)

=62x37-27x52

=2294-1404

=890

b: 1994x867+1995x133

=1994x867+1994x133+133

=1994x(867+133)+133

=1994x1000+133

=1994000+133

=1994133

Làm giúp mik rồi mik tik cho ạ

Bài 5:

Đặt \(G=\overline{ab,c}\)

=>\(G\times10=\overline{abc}\)

\(\overline{abc}+\overline{ab,c}=502,7\)

=>G+10G=502,7
=>11G=502,7

=>G=45,7

=>a=4; b=5; c=7

Bài 4: Đặt \(G=\overline{a,b}\)

=>\(10\times G=\overline{ab}\)

Sửa đề: \(\overline{ab}+\overline{a,b}=16,5_{\overline{}}\)

=>G+10G=16,5

=>11G=16,5

=>G=1,5

=>\(\overline{a,b}=1,5\)

=>a=1; b=5

Bài 2:

a: \(\overline{0,abc}\times100=6,2\times10+7,5\)

=>\(\overline{ab,c}=62+7,5=69,5\)

=>a=6; b=9; c=5

b: \(\overline{0,abc}\times100=8,1\times10+4,4\)

=>\(\overline{ab,c}=81+4,4=85,4\)

=>a=8; b=5; c=4

Bài 1:

a: \(\overline{a,87}+\overline{2,b2}=a+0,87+2+0,1b+0,02=a+0,1b+2,89\)

\(\overline{a,b}+2,89=a+0,1b+2,89\)

Do đó: \(\overline{a,87}+\overline{2,b2}=\overline{a,b}+2,89\)

b: \(\overline{a,bc}+20,04+28,63=a+0,1b+0,01c+48,67\)

\(\overline{3a,81}+\overline{4,b5}+\overline{13,9c}=30,81+a+4,05+0,01b+13,9+0,01c\)

=a+0,01b+0,01c+48,76>a+0,1b+0,01c+48,67

=>\(\overline{3a,81}+\overline{4,b5}+\overline{13,9c}>\overline{a,bc}+20,04+28,63\)

c: M=20,09x20,13

=(20,11-0,02)x(20,11+0,02)

=20,11x20,11-0,02x0,02

=N-0,02x0,02

=>M<N

\(N=\frac{1}{1.5}+\frac{1}{5.10}+\frac{1}{10.15}+\frac{1}{15.20}+...+\frac{1}{2005.2010}\)

\(N=\frac{1}{5}.\left(1-\frac{1}{5}+\frac{1}{5}-\frac{1}{10}+\frac{1}{10}-\frac{1}{15}+\frac{1}{15}-\frac{1}{20}+...+\frac{1}{2005}-\frac{1}{2010}\right)\)

\(N=\frac{1}{5}.\left(1-\frac{1}{2010}\right)\)

\(N=\frac{1}{5}.\frac{2009}{2010}\)

\(N=\frac{2009}{10050}\)

45 x 16 - 17                        =45 x (15+1) -17                =        45 x 15 +45 -17         =45 x 15 +28      =1

45 x 15 +28                           GIỮ NGUYÊN                  =         giữ nguyên            = giữ nguyên

Nè bạn k đi