a) Ta có: \(\dfrac{x}{y}=\dfrac{20}{9}\Rightarrow\dfrac{x}{20}=\dfrac{y}{9}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x}{20}=\dfrac{y}{9}=\dfrac{x-y}{20-9}=\dfrac{-44}{11}=-4\) 

\(\Rightarrow\left\{{}\begin{matrix}x=20\cdot-4=-80\\y=-4\cdot9=-36\end{matrix}\right.\)

b) \(\dfrac{x}{y}=2\dfrac{1}{2}\Rightarrow\dfrac{x}{y}=\dfrac{5}{2}\Rightarrow\dfrac{x}{5}=\dfrac{y}{2}\)

Áp dụng tính chất dãy tỉ số bằng nhau ta có:

\(\dfrac{x}{5}=\dfrac{y}{2}\Rightarrow\dfrac{x+y}{5+2}=\dfrac{40}{7}\) 

\(\Rightarrow\left\{{}\begin{matrix}\text{x}=\dfrac{40}{7}\cdot5=\dfrac{200}{7}\\y=\dfrac{40}{7}\cdot2=\dfrac{80}{7}\end{matrix}\right.\)

Làm mỗi ý a,b cũng được ạ

c: Áp dụng tính chất của dãy tỉ số bằng nhau, ta được:

\(\dfrac{x}{3}=\dfrac{y}{16}=\dfrac{3x-y}{3\cdot3-16}=\dfrac{70}{-7}=-10\)

=>\(x=-10\cdot3=-30;y=-10\cdot16=-160\)

d: Đặt \(\dfrac{x}{2}=\dfrac{y}{7}=k\)

=>x=2k; y=7k

x*y=56

=>\(2k\cdot7k=56\)

=>\(14k^2=56\)

=>\(k^2=4\)

TH1: k=2

=>\(x=2\cdot2=4;y=7\cdot2=14\)

TH2: k=-2

=>\(x=-2\cdot2=-4;y=-2\cdot7=-14\)

a;80x-64=160

80x=224

x=14/5

b;x-4=42:6

x-4=7

x=11

c;40-x=16*2

40-x=32

x=8

d;20-x=8:4

20-x=2

x=18

`# \text {Ryo}`

`a)`

`80x - 2^2 . 2^4 = 160`

`\Rightarrow 80x - 2^6 = 160`

`\Rightarrow 80x - 64 = 160`

`\Rightarrow 80x = 224`

`\Rightarrow x = 224 \div 80`

`\Rightarrow x = 2,8`

Vậy, `x = 2,8`

`b)`

`(x - 4).6 = 42`

`\Rightarrow x - 4 = 42 \div 6`

`\Rightarrow x - 4 = 7`

`\Rightarrow x = 7 + 4`

`\Rightarrow x = 11`

Vậy, `x = 11`

`c)`

`(40 - x) \div 2 = 16`

`\Rightarrow 40 - x = 16 . 2`

`\Rightarrow 40 - x = 32`

`\Rightarrow x = 40 - 32`

`\Rightarrow x = 8`

Vậy, `x = 8`

`d)`

`(20 - x) . 4 = 8`

`\Rightarrow 20 - x = 8 \div 4`

`\Rightarrow 20 - x = 2`

`\Rightarrow x = 20 - 2`

`\Rightarrow x = 18`

Vậy, `x = 18.`

cú tuii

2 x 2 + 2 x 2 + 2 - 2 x 2 = 4 + 4 + 2 - 4

                                    = 6

đáp án A là đúng

A nha bạn

2 x 2 + 2 x 2 + 2 - 2 x 2 = 6

vậy ta khoanh vào ý A

a) 2.x - 16 = 40 + x

=> 2.x - x = 40 + 16

x = 56

b) 16 - 2.x = 40 - 3.x

=> -2x + 3.x = 40 -16

x = 24

c) 6.(x-1) - 5.x = 15

6x -6 - 5.x = 15

6x-5x - 6 = 15

x - 6 = 15

x = 21

d) 2.(4.x-2) - 7.x = 16

8x - 4 - 7x = 16

8x-7x - 4 = 16

x - 4 = 16

x = 20

\(a,2x-16=40+x\)

\(\Rightarrow2x-x=40+16\)

\(\Rightarrow x=56\)

\(b,16-2x=40-3x\)

\(\Rightarrow-2x+3x=40-16\)

\(\Rightarrow x=24\)

\(c,6.\left(x-1\right)-5.x=15\)

\(\Rightarrow6x-6-5x=15\)

\(\Rightarrow x=21\)

\(d,2.\left(4x-2\right)-7.x=16\)

\(\Rightarrow8x-4-7x=16\)

\(\Rightarrow x=20\)

a, 2 . x - 16 = 40 + x

  2x - x = 40 + 16

 x = 56

Vậy x = 56

b,16 - 2 . x = 40 - 3 . x 

- 2 .x + 3 . x = 40 - 16

x = 24

Vậy x = 24

c, 6 . ( x - 1 ) - 5 . x = 15

6 . x - 6 - 5. x = 15

x =21

d, 2 . ( 4 . x - 2 ) - 7 . x = 16

8 . x - 4 - 7 . x = 16

x = 20

\(e,112-45+5x=87\)

\(67+5x=87\)

\(5x=20\)

\(x=4\)

\(f,6^2+64:\left(x-1\right)=52\)

\(36+64:\left(x+1\right)=52\)

\(64:\left(x+1\right)=16\)

\(x+1=4\)

\(x=3\)

\(g,\left(55-x\right)\left(2x-44\right)=0\)

\(\Rightarrow\hept{\begin{cases}55-x=0\\2x-44=0\end{cases}}\)

\(\Rightarrow\hept{\begin{cases}x=55\\x=22\end{cases}}\)

Vậy ....

\(h,x^2+4=13\)

\(x^2=9\)

\(x^2=\pm3^2\)

\(\Rightarrow x=\pm3\)

\(i,2\left(x+1\right)^3=16\)

\(\left(x+1\right)^3=8\)

\(\left(x+1\right)^3=2^3\)

\(\Rightarrow x+1=2\)

\(x=1\)

\(g,150-5\left(x-2\right)^2=25\)

\(5\left(x-2\right)^2=125\)

\(\left(x-2\right)^2=25\)

\(\left(x-2\right)^2=\pm5^2\)

\(\Rightarrow\hept{\begin{cases}x-2=5\\x-2=\left(-5\right)\end{cases}\Rightarrow\hept{\begin{cases}x=7\\x=\left(-3\right)\end{cases}}}\)

Vậy .... 

a:16

ai tk mình mình tk lại

A : 6

ai thấy đúng tích đi

Đáp án: a

Bài 1

a) \(5\times72\times10\times2=\left(5\times2\times10\right)\times72=100\times72=7200\) 

b) \(40\times125=5\times\left(8\times125\right)=5\times1000=5000\) 

c) \(16\times6\times25=4\times4\times6\times25=\left(4\times6\right)\times\left(4\times25\right)=24\times100=2400\) Bài 2:

a) \(24\times57+43\times24=24\times\left(57+43\right)=24\times100=2400\) 

b) \(12\times19+80\times12+12=12\times\left(19+80+1\right)=12\times100=1200\) 

c) \(\left(36\times15\times169\right)\div\left(5\times18\times13\right)\) 

 \(=\left(18\times2\times3\times5\times13\times13\right)\div\left(5\times18\times13\right)\) 

\(=\left(2\times3\times13\right)\times\left(18\times5\times13\right)\div\left(5\times18\times13\right)\) 

\(=2\times3\times13\)

\(=78\)

d) \(\left(44\times52\times60\right)\div\left(11\times13\times15\right)\) 

\(=\left(4\times11\times4\times13\times4\times15\right)\div\left(11\times13\times15\right)\)

\(=\left(4\times4\times4\right)\times\left(11\times13\times15\right)\div\left(11\times13\times15\right)\)

\(=4\times4\times4\)

\(=64\)

Bài 3:

a) \(x-280\div35=5\times54\) 

                \(x-8=270\) 

                      \(x=270+8\) 

                      \(x=278\) 

b) \(\left(x-280\right)\div35=54\div4\) 

    \(\left(x-280\right)\div35=\dfrac{27}{2}\) 

               \(x-280=\dfrac{27}{2}\times35\) 

                \(x-280=\dfrac{945}{2}\) 

                          \(x=\dfrac{945}{2}+280\) 

                          \(x=\dfrac{1505}{2}\) 

c) \(\left(x-128+20\right)\div192=0\) 

                 \(x-128+20=0\times192\) 

                \(x-128+20=0\) 

                        \(x-128=0-20\) 

                        \(x-128=-20\)

                                  \(x=-20+128\) 

                                 \(x=108\) 

d) \(4\times\left(x+200\right)=460+85\times4\) 

    \(4\times\left(x+200\right)=460+340\) 

    \(4\times\left(x+200\right)=800\) 

             \(x+200=800\div4\) 

             \(x+200=200\) 

                      \(x=200-200\) 

                      \(x=0\) 

Bài 4:

a) \(\dfrac{7}{12}-\dfrac{5}{12}=\dfrac{2}{12}=\dfrac{1}{6}\) 

b) \(\dfrac{8}{11}+\dfrac{19}{11}=\dfrac{27}{11}\) 

c) \(\dfrac{3}{8}+\dfrac{5}{12}=\dfrac{9}{24}+\dfrac{10}{24}=\dfrac{19}{24}\) 

d) \(\dfrac{3}{4}+\dfrac{7}{12}=\dfrac{9}{12}+\dfrac{7}{12}=\dfrac{16}{12}=\dfrac{4}{3}\) 

Bài 5:

a) \(x-\dfrac{6}{7}=\dfrac{5}{2}\) 

           \(x=\dfrac{5}{2}+\dfrac{6}{7}\) 

           \(x=\dfrac{47}{14}\) 

b) \(\dfrac{12}{7}\div x+\dfrac{2}{3}=\dfrac{7}{5}\) 

            \(\dfrac{12}{7}\div x=\dfrac{7}{5}-\dfrac{2}{3}\) 

             \(\dfrac{12}{7}\div x=\dfrac{11}{15}\) 

                       \(x=\dfrac{12}{7}\div\dfrac{11}{15}\) 

                        \(x=\dfrac{180}{77}\)

`@` `\text {Ans}`

`\downarrow`

`1,`

`a)`

`5 \times 72 \times 10 \times 2`

`= 5 \times 2 \times 10 \times 72`

`= 10 \times 10 \times 72`

`= 100 \times 72`

`= 7200`

`b)`

`40 \times 125`

`= 4 \times 10 \times 25 \times 5`

`= (5 \times 10) \times (4 \times 25)`

`= 50 \times 100`

`= 5000`

`c)`

`4 \times 2021 \times 25`

`= (4 \times 25) \times 2021`

`= 100 \times 2021`

`= 202100`

`d)`

`16 \times 6 \times 25`

`= 4 \times 4 \times 6 \times 25`

`= (4 \times 25) \times 4 \times 6`

`= 100 \times 24`

`= 2400`

`2,`

`a)`

`24 \times 57 + 43 \times 24`

`= 24 \times (57+43)`

`= 24 \times 100`

`= 2400`

`b)`

`12 \times 19 + 80 \times 12 +12`

`= 12 \times (19 + 80 + 1)`

`= 12 \times 100`

`= 1200`

`c)`

`(36 \times 15 \times 169) \div (5 \times 18 \times 13)`

`= 36 \times 15 \times 169 \div 5 \div 18 \div 13`

`= 6 \times 6 \times 3 \times 5 \times 13 \times 13 \div 5 \div 3 \times 6 \div 13`

`= (6 \div 6) \times (3 \div 3) \times (5 \div 5) \times (13 \div 13) \times 6 \times 13`

`= 6 \times 13`

`= 78`

`d)`

`(44 \times 52 \times 60) \div ( 11 \times 13 \times 15)`

`= 44 \times 52 \times 60 \div 11 \div 13 \div 15`

`= 4 \times 11 \times 13 \times 4 \times 15 \times 4 \div 11 \div 13 \div 15`

`= (11 \div 11) \times (13 \div 13) \times (15 \div 15) \times 4 \times 4 \times`

`= 4 \times 4 \times 4`

`= 64`

`3,`

`a)`

`x - 280 \div 35 = 5 \times 54`

`x - 8 = 270`

`x = 270 + 8`

`x = 278`

`b)`

`(x - 280) \div 35 = 54 \div 4`

`(x - 280) \div 35 = 13,5`

`x - 280 = 13,5 \times 35`

`x - 280 = 472,5`

`x = 472,5 + 280`

`x = 752,5`

`c)`

`(x - 128 + 20) \div 192 = 0`

`x - 128 + 20 = 0 \times 192`

`x - 128 + 20 = 0`

`x - 108 = 0`

`x = 0 + 108`

`x = 108`

`d)`

`4 \times (x + 200) = 460 + 85 \times 4`

`4 \times (x+200) = 460 + 340`

`4 \times (x+200) = 800`

`x + 200 = 800 \div 4`

`x + 200 = 200`

`x = 200 - 200`

`x = 0`

`4,`

`a)`

`7/12 - 5/12`

`= (7 - 5)/12`

`= 2/12`

`= 1/6`

`b)`

`8/11 + 19/11`

`= (8+19)/11`

`= 27/11`

`c)`

`3/8 + 5/12`

`= 9/24 + 10/24`

`= 19/24`

`d)`

`3/4 + 7/12`

`= 9/12 + 7/12`

`= 16/12`

`= 4/3`

`5,`

`a)`

`x - 6/7 = 5/2`

`x = 5/2 + 6/7`

`x = 47/14`

`b)`

`12/7 \div x + 2/3 = 7/5`

`12/7 \div x = 7/5 - 2/3`

`12/7 \div x = 11/15`

`x = 12/7 \div 11/15`

`x = 180/77`

`@` `\text {Kaizuu lv uuu}`