\(a,\frac{1995}{1996}.\frac{19961996}{19311931}.\frac{193119311931}{199519951995}\)                               \(c,\frac{1997.1996-1}{1995.1997+1996}\)

\(=\frac{1995}{1996}.\frac{1996}{1931}.\frac{1931}{1995}\)                                                           \(=\frac{1997.\left(1995+1\right)-1}{1995.1997+1996}\)

\(=\frac{1995.1996.1931}{1996.1931.1995}\)                                                                   \(=\frac{1997.1995+1997-1}{1997.1995+1996}\)

\(=1\)                                                                                                     \(=\frac{1997.1995+1996}{1995.1997+1996}\)

                                                                                                                      \(=1\)

Ý (a) giống ý (b)

Ý (c) giống ý (d)

TA CÓ:

a; 1313/2121=13/21    165165/143143=165/143       424242/151515=42/15

=> 13/21 x 165/143 x 42/15=13 x 165 x 42/21 x 143 x 15=22/11=2

b,1995/1995 x 19961996/19931993 x 199319931993/199519951995

=1 x 1996/1993 x 1993/1995

=1 x 1996/1995

=1996/1995

a, 1313/2121 x 165165/143143 x 424242/151515

=13/21 x 165/143 x 13/5

=2

Trl :

bạn kia làm đúng rồi nhé 

    hk tốt nhé bạn @

a) 1313/2121 . 165165/143143 . 424242/151515

= 13/21 . 15/13 . 14/5 

= 2 

Ps: Rút gọn tới tối giản r tính dễ hơn ế. ;) 

\(\left(\frac{151515}{60606}+\frac{151515}{121212}+\frac{151515}{202020}+\frac{151515}{303030}+\frac{151515}{424242}\right)\times\frac{28}{15}\)

\(=\left(\frac{5}{2}+\frac{5}{4}+\frac{3}{4}+\frac{1}{2}+\frac{5}{14}\right)\times\frac{28}{15}\)

\(=\frac{75}{14}\times\frac{28}{15}\)

\(=10\)

= ( 1/4 + 5/4 + 3/4 + 1/2 + 5/14) . 28/15
= [ 9/4 +( 7/14 + 5/14)] . 28/15
=        (9/4 + 6/7) . 28/15
= 87/28 . 28/15 = 87/15 = 29/5
 

= 10,ai k mk thì mk k lại

Trloi chi tiết giúp tớ

=13/21*15/13*14/5

=5/7*14/5

=2

=\(\dfrac{13\cdot101}{21\cdot101}\)*\(\dfrac{165\cdot1001}{143\cdot1001}\)*\(\dfrac{42\cdot10101}{15\cdot10101}\)

=\(\dfrac{13}{21}\)*\(\dfrac{165}{143}\)*\(\dfrac{42}{15}\)

=\(\dfrac{13\cdot15\cdot11\cdot21\cdot2}{21\cdot13\cdot11\cdot15}\)=2

\(\frac{1}{2}\cdot\frac{1}{3}+\frac{1}{3}\cdot\frac{1}{4}+\frac{1}{4}\cdot\frac{1}{5}+\frac{1}{5}\cdot\frac{1}{6}+\frac{1}{6}\cdot\frac{1}{7}+\frac{1}{7}\cdot\frac{1}{8}+\frac{1}{8}\cdot\frac{1}{9}\)

\(=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+\frac{1}{4\cdot5}+\frac{1}{5\cdot6}+\frac{1}{6\cdot7}+\frac{1}{7\cdot8}+\frac{1}{8\cdot9}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\)

\(=\frac{1}{2}-\frac{1}{9}=\frac{7}{18}\)

\(\frac{1}{2}\cdot\frac{1}{3}+\frac{1}{3}\cdot\frac{1}{4}+...+\frac{1}{8}\cdot\frac{1}{9}\)

\(=\frac{1}{2\cdot3}+\frac{1}{3\cdot4}+...+\frac{1}{8\cdot9}\)

\(=\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{8}-\frac{1}{9}\)

 \(=\frac{1}{2}-\frac{1}{9}\)

            * LÀM NỐT *

                              #Louis

1/2.1/3+1/3.1/4+1/4.1/5+...+1/8.1/9

=1/2.3=1/3.4+1/4.5+...+1/8.9\

=1/2-1/3+1/3-1/4=1/4-1/5+...+1/8.1/9

=1/2-1/9

=9/18-2/18

=7/18

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