a)\(\dfrac{2}{3}.\dfrac{4}{5}+\dfrac{1}{3}.\dfrac{4}{5}=\left(\dfrac{2}{3}+\dfrac{1}{3}\right).\dfrac{4}{5}=1.\dfrac{4}{5}=\dfrac{4}{5}\)

b)\(\dfrac{2}{3}.\dfrac{4}{5}-\dfrac{1}{3}.\dfrac{4}{5}=\left(\dfrac{2}{3}-\dfrac{1}{3}\right).\dfrac{4}{5}=\dfrac{1}{3}.\dfrac{4}{5}=\dfrac{4}{15}\)

a) \(\dfrac{2}{3}\times\dfrac{4}{5}+\dfrac{1}{3}\times\dfrac{4}{5}=\dfrac{4}{5}\times\left(\dfrac{2}{3}+\dfrac{1}{3}\right)=\dfrac{4}{5}\times1=\dfrac{4}{5}\)

b) \(\dfrac{2}{3}\times\dfrac{4}{5}-\dfrac{1}{3}\times\dfrac{4}{5}=\dfrac{4}{5}\times\left(\dfrac{2}{3}-\dfrac{1}{3}\right)=\dfrac{4}{5}\times\dfrac{1}{3}=\dfrac{4}{15}\)

c) \(\dfrac{1}{2}:\dfrac{3}{4}+\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}\times\dfrac{4}{3}+\dfrac{1}{6}\times\dfrac{4}{3}=\dfrac{4}{3}\times\left(\dfrac{1}{2}+\dfrac{1}{6}\right)=\dfrac{4}{3}\times\dfrac{2}{3}=\dfrac{8}{9}\)

d) \(\dfrac{1}{2}:\dfrac{3}{4}-\dfrac{1}{6}:\dfrac{3}{4}=\dfrac{1}{2}\times\dfrac{4}{3}-\dfrac{1}{6}\times\dfrac{4}{3}=\dfrac{4}{3}\left(\dfrac{1}{2}-\dfrac{1}{6}\right)=\dfrac{4}{3}\times\dfrac{1}{3}=\dfrac{4}{9}\)

`@` ` \text {Ans}`

`\downarrow`

`a,`

`1/4+3/4*x=3/2-x`

`=> 1/4 + 3/4x - 3/2 + x = 0`

`=> (1/4 - 3/2) + (3/4x + x) = 0`

`=> -5/4 + 7/4x = 0`

`=> 7/4x = 5/4`

`=> x = 5/4 \div 7/4`

`=> x = 5/7`

Vậy, `x=5/7`

`b,`

`3/5*x-1/4=1/10*x-1/2`

`=> 3/5x - 1/4 - 1/10x + 1/2 = 0`

`=> (3/5x - 1/10x) + (-1/4 + 1/2)=0`

`=> 1/2x + 1/4 = 0`

`=> 1/2x = -1/4`

`=> x = -1/4 \div 1/2`

`=> x = -1/2`

Vậy, `x=-1/2`

`c,`

`3x-3/5=x-1/4`

`=> 3x - 3/5 - x + 1/4 = 0`

`=> (3x - x) - (3/5 - 1/4) = 0`

`=> 2x - 7/20 = 0`

`=> 2x = 0,35`

`=> x = 0,35 \div 2`

`=> x = 7/40`

Vậy, `x=7/40`

`d,`

`3/2*x-2/5=1/3*x-1/4`

`=>  3/2x - 2/5 - 1/3x + 1/4 = 0`

`=> (3/2x - 1/3x) - (2/5 - 1/4) = 0`

`=> 7/6x - 3/20 = 0`

`=> 7/6x = 3/20`

`=> x = 3/20 \div 7/6`

`=> x = 9/70`

Vậy, `x=9/70`

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

D

`=>` Đáp án: `D`

Ta có tập hợp các mặt từ `1` đến `6` là:

   `X = {1; 2; 3; 4; 5; 6}`

câu D đúng 

D. X = {1; 2; 3; 4; 5; 6}

a,

=x³+1-(x³-1)

=x³+1-x³+1

=2

b,

tự làm nha bạn

a: \(\left|-x+\frac25\right|+\frac12=3,5\)

=>\(\left|x-\frac25\right|=3,5-0,5=3\)

=>\(\left[\begin{array}{l}x-\frac25=3\\ x-\frac25=-3\end{array}\right.\Rightarrow\left[\begin{array}{l}x=3+\frac25=\frac{17}{5}\\ x=-3+\frac25=-\frac{13}{5}\end{array}\right.\)

b: \(\frac{21}{5}+3:\left|\frac{x}{4}-\frac23\right|=6\)

=>\(3:\left|\frac14x-\frac23\right|=6-\frac{21}{5}=\frac95\)

=>\(\left|\frac14x-\frac23\right|=3:\frac95=3\cdot\frac59=\frac53\)

=>\(\left[\begin{array}{l}\frac14x-\frac23=\frac53\\ \frac14x-\frac23=-\frac53\end{array}\right.\Rightarrow\left[\begin{array}{l}\frac14x=\frac23+\frac53=\frac73\\ \frac14x=-\frac53+\frac23=-\frac33=-1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac73\cdot4=\frac{28}{3}\\ x=-1\cdot4=-4\end{array}\right.\)

c: 7,5-3|5-2x|=-4,5

=>3|5-2x|=7,5+4,5=12

=>3|2x-5|=12

=>|2x-5|=4

=>\(\left[\begin{array}{l}2x-5=4\\ 2x-5=-4\end{array}\right.\Rightarrow\left[\begin{array}{l}2x=9\\ 2x=1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac92\\ x=\frac12\end{array}\right.\)

d: \(\frac13-\left|\frac54-2x\right|=\frac14\)

=>\(\left|\frac54-2x\right|=\frac13-\frac14=\frac{1}{12}\)

=>\(\left|2x-\frac54\right|=\frac{1}{12}\)

=>\(\left[\begin{array}{l}2x-\frac54=\frac{1}{12}\\ 2x-\frac54=-\frac{1}{12}\end{array}\right.\Rightarrow\left[\begin{array}{l}2x=\frac54+\frac{1}{12}=\frac{16}{12}=\frac43\\ 2x=\frac54-\frac{1}{12}=\frac{15}{12}-\frac{1}{12}=\frac{14}{12}=\frac76\end{array}\right.\)

=>\(\left[\begin{array}{l}x=\frac23\\ x=\frac{7}{12}\end{array}\right.\)

e: \(\frac{21}{5}+3:\left|\frac{x}{4}-\frac23\right|=6\)

=>\(3:\left|\frac14x-\frac23\right|=6-\frac{21}{5}=\frac95\)

=>\(\left|\frac14x-\frac23\right|=3:\frac95=3\cdot\frac59=\frac53\)

=>\(\left[\begin{array}{l}\frac14x-\frac23=\frac53\\ \frac14x-\frac23=-\frac53\end{array}\right.\Rightarrow\left[\begin{array}{l}\frac14x=\frac23+\frac53=\frac73\\ \frac14x=-\frac53+\frac23=-\frac33=-1\end{array}\right.\Rightarrow\left[\begin{array}{l}x=\frac73\cdot4=\frac{28}{3}\\ x=-1\cdot4=-4\end{array}\right.\)