= \(\frac{12}{15}\) +\(\frac{12}{35}\)+\(\frac{12}{63}\)+\(\frac{12}{99}\)

= 12 x (\(\frac{1}{15}\)+\(\frac{1}{35}\)+\(\frac{1}{63}\)+\(\frac{1}{99}\))

= 12 x ( \(\frac{1}{3x5}\)+\(\frac{1}{5x7}\)+\(\frac{1}{7x9}\)+\(\frac{1}{9x11}\))

= 12 x \(\frac{1}{2}\) x    ( \(\frac{1}{3}\)-\(\frac{1}{5}\)+\(\frac{1}{5}\)-\(\frac{1}{7}\)+\(\frac{1}{7}\)-\(\frac{1}{9}\)+\(\frac{1}{9}\)-\(\frac{1}{11}\))

= 6 x (   \(\frac{1}{3}\) -  \(\frac{1}{11}\))

=  6 x \(\frac{8}{33}\)

= \(\frac{48}{33}\)=\(\frac{16}{11}\)

      Nhớ tk nha

lấy tất cả chia cho 1010

\(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

\(=1212.\left(\frac{1}{15.101}+\frac{1}{35.101}+\frac{1}{63.101}+\frac{1}{99.101}\right)\)

\(=12.101.\frac{1}{101}.\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=6.\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right)\)

\(=6.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(=6.\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=6.\left(\frac{11}{33}-\frac{3}{33}\right)\)

\(=6.\frac{8}{33}\)

\(=\frac{16}{11}\)

\(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

\(=\frac{12}{15}+\frac{12}{35}+\frac{12}{63}+\frac{12}{99}\)

\(=12.\left(\frac{1}{15}+\frac{1}{35}+\frac{1}{63}+\frac{1}{99}\right)\)

\(=12.\left(\frac{1}{3.5}+\frac{1}{5.7}+\frac{1}{7.9}+\frac{1}{9.11}\right)\)

\(=12.\frac{1}{2}.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+\frac{1}{7}-\frac{1}{9}+\frac{1}{9}-\frac{1}{11}\right)\)

\(=6.\left(\frac{1}{3}-\frac{1}{11}\right)\)

\(=6.\frac{8}{33}\)

\(=\frac{16}{11}\)

_Chúc bạn học tốt_

Mua ha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihi ha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihi ha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihi ha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihiha ha ha ha hihihihihihihihihihi

tại sao phải chia cho 1/2 z bn ?
 

\(\dfrac{1212}{1515}+\dfrac{1212}{3535}+\dfrac{1212}{6363}+\dfrac{1212}{9999}\)

=\(\dfrac{12}{15}+\dfrac{12}{35}+\dfrac{12}{63}+\dfrac{12}{99}\)

=\(\dfrac{16}{11}\)

Giải:

\(\dfrac{1212}{1515}+\dfrac{1212}{3535}+\dfrac{1212}{6363}+\dfrac{1212}{9999}\) 

\(=\dfrac{12}{15}+\dfrac{12}{35}+\dfrac{12}{63}+\dfrac{12}{99}\) 

\(=12.\left(\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+\dfrac{1}{9.11}\right)\) 

\(=12.\dfrac{1}{2}.\left(\dfrac{2}{3.5}+\dfrac{2}{5.7}+\dfrac{2}{7.9}+\dfrac{2}{9.11}\right)\) 

\(=6.\left(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\right)\) 

\(=6.\left(\dfrac{1}{3}-\dfrac{1}{11}\right)\) 

\(=6.\dfrac{8}{33}\) 

\(=\dfrac{16}{11}\)

\(=\dfrac{12}{15}+\dfrac{12}{35}+\dfrac{12}{63}+\dfrac{12}{99}=12\cdot\left[\dfrac{1}{15}+\dfrac{1}{35}+\dfrac{1}{63}+\dfrac{1}{99}\right]=12\cdot\left[\dfrac{1}{3\cdot5}+\dfrac{1}{5\cdot7}+\dfrac{1}{7\cdot9}+\dfrac{1}{9\cdot11}\right]=12\cdot\dfrac{1}{2}\cdot\left[\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{11}\right]=6\cdot\left[\dfrac{1}{3}-\dfrac{1}{11}\right]=6\cdot\dfrac{8}{33}=\dfrac{48}{33}=\dfrac{16}{11}\)

a)=4.25x(58.47+41.53)-125

=4.25x100-125

=425-100

=325

rút gọn PS thì ta có

B = 4/5 + 12/35 + 4/21 + 4/33

B = 16/11

\(B=\frac{4}{5}+\frac{12}{35}+\frac{4}{21}+\frac{4}{33}\)

\(B=\left(\frac{28}{35}+\frac{12}{35}\right)+\left(\frac{44}{231}+\frac{28}{231}\right)\)

\(B=\frac{8}{7}+\frac{24}{77}\)

\(B=\frac{88}{77}+\frac{24}{77}=\frac{112}{77}=\frac{16}{11}\)

16/11

GOOB BYE

\(1,\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}=\frac{12}{15}+\frac{12}{35}+\frac{12}{63}+\frac{12}{99}=6\left(\frac{2}{15}+\frac{2}{35}+\frac{2}{63}+\frac{2}{99}\right)=6\left(\frac{2}{3.5}+\frac{2}{5.7}+\frac{2}{7.9}+\frac{2}{9.11}\right).Tacocongthuc:\frac{1}{n}-\frac{1}{n+k}=\frac{k}{n\left(n+k\right)}\Rightarrow\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}=6\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-.....-\frac{1}{11}\right)=6\left(\frac{1}{3}-\frac{1}{11}\right)=\frac{48}{33}=\frac{16}{11}\)

\(2,\left(x+1\right)+\left(x+2\right)+.....+\left(x+211\right)=211x+\left(1+2+....+211\right)=211x+\frac{212.211}{2}=211x+22366=23632\Leftrightarrow211x=23632-22366=1266\Leftrightarrow x=6\)

a, \(14:\left(4\frac{2}{3}:1\frac{5}{9}\right)+14:\left(\frac{2}{3}+\frac{8}{9}\right)\)

=> \(14:\frac{28}{9}+14:\frac{14}{9}=>14.\frac{9}{28}+14.\frac{9}{14}\)

=> 14. ( \(\frac{9}{28}+\frac{9}{14}\) )

=> \(14.\frac{27}{28}=\frac{419}{28}\)

b, \(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

=> \(\frac{4}{5}+\frac{12}{35}+\frac{4}{21}+\frac{4}{33}\)

=> \(\frac{8}{7}+\frac{24}{77}=\frac{16}{11}\)

bài 2 :

( x + 1 ) + ( x + 2 ) + ... + ( x + 211 ) = 23632

=> ( x + x + x + ... + x ) + ( 1 + 2 + 3 + ... + 211 ) = 23632

=> 211x + 22366 = 23632

=> 211x = 23632 - 22366

=> 211x = 1266

=> x = 1266 : 211

x = 6

\(\frac{1212}{1515}+\frac{1212}{3535}+\frac{1212}{6363}+\frac{1212}{9999}\)

\(=1212.\left(\frac{1}{1515}+\frac{1}{3535}+\frac{1}{6363}+\frac{1}{9999}\right)\)

Sau đó tự tính rồi làm típ nha 

Study well 

Ta có : 1212/3535=12/35 ; 1212/9999=12/99

Từ đề bài => = 12/15 +12/35 +12/63 +12/99

                    = 6 x ( 2/15 + 2/35 +2/63+2/99 )

                    = 6 x ( 2/3x5 + ....+ 2/9x11)

                    = 6 x ( 1/3 - 1/5 +....+1/9 - 1/11)

                    = 6 x ( 1/3 - 1/11)

                    = 6 x 8/33 = 48/33

ai giúp zới. mai đi hok rùi

48/33