A=1/18 + 1/36 + ... + 1/29700

A= 1/3.6 + 1/3.12 + ... 1/3.9900

A= 1/3 . 1/6 + 1/3 . 1/12 + ... + 1/3 . 1/9900

A= 1/3 .(1/2.3 +1/3.4 + ... + 1/99.100)

A= 1/3 .(1/2 - 1/3 +1/3 -1/4 + ... + 1/99 - 1/100)

A= 1/3 .(1/2 - 1/100)

A= 1/3 . 49/100

A= 49/300

\(a,\frac{15}{2}-\left(\frac{x}{2}-\frac{3}{4}\right)=\frac{5}{26}\)

\(\frac{x}{2}-\frac{3}{4}=\frac{15}{2}-\frac{5}{26}\)

\(\frac{x}{2}-\frac{3}{4}=39\)

\(\frac{x}{2}=39+\frac{3}{4}\)

\(\frac{x}{2}=\frac{159}{4}\)

\(\Rightarrow\frac{2.x}{4}=\frac{159}{4}\)

\(\Rightarrow2.x=159\)

\(\Rightarrow x=159:2=\frac{159}{2}\)

\(\frac{12}{18}+\frac{1}{3}+\frac{1}{7}+\frac{2}{8}+\frac{27}{36}+\frac{42}{49}\)

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

\(=\left(\frac{2}{3}+\frac{1}{3}\right)+\left(\frac{1}{7}+\frac{6}{7}\right)+\left(\frac{1}{4}+\frac{3}{4}\right)\)

\(=1+1+1\)

\(=3\)

7/8 chia (2/9-1/8)+7/8 CHIA (1/36-5/12

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

=21/4+(-7/8)

=35/8

232

\(\frac{32}{99}\)

Máy tính bấm auto ra ... =))

\(A=\frac{1}{18}+\frac{1}{36}+\frac{1}{60}+...+\frac{1}{168}\)

 \(\frac{1}{3}A=\frac{1}{54}+\frac{1}{108}+...+\frac{1}{504}\)

\(\frac{1}{3}A=\frac{1}{6.9}+\frac{1}{9.12}+...+\frac{1}{21.24}\)

\(=\frac{1}{6}-\frac{1}{9}+\frac{1}{9}-\frac{1}{12}+...+\frac{1}{21}-\frac{1}{24}\)

\(=\frac{1}{6}-\frac{1}{24}\)

\(=\frac{4-1}{24}=\frac{3}{24}=\frac{1}{8}\)

=> \(A=\frac{1}{8}:\frac{1}{3}\)\(=\frac{3}{8}\)

a) \(\frac{-1}{2}+\frac{-1}{9}-\frac{-3}{5}+\frac{1}{2006}-\frac{-2}{7}-\frac{7}{18}+\frac{4}{35}\)

\(=\left(\frac{-1}{2}-\frac{1}{9}-\frac{7}{18}\right)+\left(\frac{3}{5}+\frac{4}{35}\right)+\frac{1}{2006}\)

\(=\left(\frac{-9}{18}-\frac{2}{18}-\frac{7}{18}\right)+\left(\frac{21}{35}+\frac{4}{35}\right)+\frac{1}{2006}\)

\(=\left(\frac{-9-2-7}{18}\right)+\left(\frac{21+4}{35}\right)+\frac{1}{2006}\)

\(=\left(\frac{-18}{18}\right)+\left(\frac{25}{35}\right)+\frac{1}{2006}\)

\(=\left(-1\right)+\frac{5}{7}+\frac{1}{2006}\)\(=\frac{-4005}{14042}\)

b) \(\frac{1}{3}-\frac{3}{4}+\frac{3}{5}+\frac{1}{2007}-\frac{1}{36}+\frac{1}{15}-\frac{2}{9}\)

\(=\left(\frac{1}{3}+\frac{1}{2007}-\frac{2}{9}\right)-\left(\frac{3}{4}+\frac{1}{36}\right)+\left(\frac{3}{5}+\frac{1}{15}\right)\)

\(=\left(\frac{669}{2007}+\frac{1}{2007}-\frac{446}{2007}\right)-\left(\frac{27}{36}+\frac{1}{36}\right)+\left(\frac{9}{15}+\frac{1}{15}\right)\)

\(=\frac{224}{2007}-\frac{28}{36}+\frac{10}{15}\)

\(=\frac{224}{2007}-\frac{1561}{2007}+\frac{1338}{2007}\)\(=\frac{1}{2007}\)

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??????

C = 1/3 + -3/4 + 3/5 + 1/57 + -1/36 + 1/15 + -2/9

C = ( 1/3 + 1/57 ) + ( -3/4 + -1/36 ) + ( 3/5 + 1/15 ) + -2/9 

C = ( 19/57 + 1/57 ) + ( -27/36 + -1/36 ) + ( 9/15 + 1/15 ) + -2/9 

C = 20/57 + -28/36 + 10/15 + -2/9 

C = 20/57 + -7/9 + 2/3 + -2/9

C = ( 20/57 + 2/3 ) + ( -7/9 + -2/9 )

C = 58/57 + -1 

C = 1/57

D = 1/2 + -1/5 + -5/7 + 1/6 + -3/35 + 1/3 + 1/41

D = ( 1/2 + 1/3 + 1/6 ) + ( -1/5 + -5/7 +-3/35 ) + 1/41

D = ( 3/6 + 2/6 + 1/6 ) + ( -7/35 + -25/35 + -3/35 ) + 1/41

D = 1 + -1 + 1/41

D = 1/41

E = -1/2 + 3/5 + -1/9 + 1/127 + -7/18 + 4/35 + 2/7 

E = ( -1/2 + -1/9 + -7/18 ) + ( 3/5 + 4/35 ) + 1/127 + 2/7

E = ( -9/18 + -2/18 + -7/18 ) + ( 21/35 + 4/35 ) + 1/127 + 2/7

E = -1 + 5/7 + 1/257 + 2/7 

E = -1 + ( 5/7 + 2/7 ) + 1/127

E = -1 + 1 + 1/127

E = 1/127

\(C=\frac{1}{3}+\frac{-3}{4}+\frac{3}{5}+\frac{1}{57}+\frac{-1}{36}+\frac{1}{15}+\frac{-2}{9}.\)

\(C=\left(\frac{1}{3}+\frac{3}{5}+\frac{1}{15}\right)-\left(\frac{3}{4}+\frac{1}{36}+\frac{2}{9}\right)+\frac{1}{57}\)

\(C=1-1+\frac{1}{57}\)

\(C=\frac{1}{57}\)

D=1/2+-1/5+-5/7+1/6+-3/35+1/3+1/41

D=(1/2+1/6+1/3)-(1/5+3/35+5/7)+1/41

D=1-1+1/41

D=1/41

E=-1/2+3/5+-1/9+1/127+-7/18+4/35+2/7

E=(3/5+4/35+2/7)-(1/2+1/9+7/18)+1/127

E=1-1+1/127

E=1/127