cách 1: 20 + 3 = 23

cách 2: 20 + (3\(^3\): 3\(^2\)) = 20 + 3 = 23

cách 3: 20 + (9.3 : 9) = 20 + 3 = 23

Cách 1: (24x45):9=1080:9=120

C1 (24 x 45):9

=1080 : 9

=120

C2 (24 x 45):9

=24 x (45:9)

=24 x 5

=120

học tốt em nhé

a)                                       b)

 4218 : ( 2 x 3)                        ( 27 x 108 ) : 9 

= 4218 : 6                              = 2916 : 9

= 703                                    = 324

C₁ :4218:(2*3)=4218:6=703

C₂ :4218:(2*3)=4218:2:3=2109:3=703

C₁:(27*108):9=2916:9=324

C₂:(27*108):9=(27:9)*108=324

\(\dfrac{2}{1\times3}+\dfrac{2}{3\times5}+\dfrac{2}{5\times7}+...+\dfrac{2}{13\times15}+\dfrac{2}{15\times17}\)

\(=1-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{13}-\dfrac{1}{15}+\dfrac{1}{15}-\dfrac{1}{17}\)

\(=1-\dfrac{1}{17}\)

\(=\dfrac{16}{17}\)

\(\dfrac{2}{1\cdot3}+\dfrac{2}{3\cdot5}+...+\dfrac{2}{15\cdot17}\)

\(=2-\dfrac{1}{3}+\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+...+\dfrac{1}{15}-\dfrac{1}{17}\)

\(=2-\dfrac{1}{17}\)

\(=\dfrac{33}{17}\)

\(=13\cdot70\cdot\left(\frac{1}{7}+\frac{1}{10}\right)=13\cdot\left(\frac{70}{7}+\frac{70}{10}\right)=13\cdot\left(10+7\right)=13\cdot17=221.\)

Vậy....

=70x13/7+70x13/10

=10x13+7x13

=130+91

=221

29-(10+29)=x-(27-9)

20-10-9=x-27+9

10-9=x-36

1=x-36

x-36=1

x=1+36

x=37

29-(10+29)=x-(27-9)

-10=x-18

-10+18=x

8=x

=>x=8

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