\(A=\dfrac{121212}{131313}+\dfrac{154154}{143143}-\left(\dfrac{2121}{2323}+\dfrac{275275}{253253}\right)\)

\(=\dfrac{12}{13}+\dfrac{14}{13}-\left(\dfrac{21}{23}+\dfrac{25}{23}\right)\)

\(=2-2=0\)

Ta thấy : 1313/2121 = 1313 : 101 = 13   , 1515 : 101 = 15   , 424242 : 30303 = 14 , 
                                      2121 : 101 = 21    1313 : 101    13     151515 : 30303  5  
 Vậy 13 x 15 x 14  =  14
          21 x 13 x 15 =  21
 Bạn k cho mình đi mình nhanh nhất với lại đúng nữa !!!

a, 12+18+24+30+36+42

=6.2+6.3+6.4+6.5+6.6+6.7

=6.(2+3+4+5+6+7)

=6.27

=162

b, mm+pp+xx+yy

=11.m+11.p+11.x+11.y

=11.(m+p+x+y)

c, 1212+2121+4242+2424

=12.101+21.101+42.101+24.101

=(12+21+42+24).101

=99.101

=9999

\(A=\frac{1}{2}×\frac{3}{4}+\frac{1}{4}×\frac{1}{2}\)

\(A=\frac{1}{2}×\left(\frac{3}{4}+\frac{1}{4}\right)\)

\(A=\frac{1}{2}×\left(\frac{3+1}{4}\right)\)

\(A=\frac{1}{2}×1\)

\(A=\frac{1}{2}\)

\(B=\frac{1212}{2121}×\frac{151515}{161616}\)

\(B=\frac{1212:101}{2121:101}×\frac{151515:10101}{161616:10101}\)

\(B=\frac{12}{21}×\frac{15}{16}\)

\(B=\frac{12×15}{21×16}\)

\(B=\frac{3×4×3×5}{3×7×4×4}\)

\(B=\frac{15}{28}\)

\(15x\frac{2121}{4343}+15x\frac{222222}{434343}\)

\(=15x\frac{21}{43}+15x\frac{22}{43}\)

\(=15x\left(\frac{21}{43}+\frac{22}{43}\right)\)

\(=15x1\)

\(=15\)

= 15 x 21/43 + 15x 22/43

= 15 x (21/43 + 22/43)

= 15 x 1 =15

\(15\cdot\frac{2121}{4343}+15\cdot\frac{222222}{434343}\) =\(15\cdot\left(\frac{2121}{4343}+\frac{222222}{434343}\right)\) =\(15\cdot\left(\frac{21}{43}+\frac{22}{43}\right)\)  =\(15\cdot\frac{43}{43}\) =\(15\cdot1=15\)   tish cho mk nhé                                                                                                                              

=2*4/5*3/4=2*3/5=6/5

`(4242×12×15)/(2121×15×20)`

`= (2xx2121×12×15)/(2121×15×20)`

`=(2×12)/20`

`= 24/20 = 6/5`

\(\dfrac{4242\times12\times15}{2121\times15\times20}=\dfrac{2121\times2\times4\times3\times15}{2121\times15\times4\times5}\\ =\dfrac{2\times3}{5}=\dfrac{6}{5}\)

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. ;)