a: Ta có: \(\left|\dfrac{2}{5}-x\right|+\dfrac{1}{2}=3.5\)

\(\Leftrightarrow\left|x-\dfrac{2}{5}\right|=3\)

\(\Leftrightarrow\left[{}\begin{matrix}x-\dfrac{2}{5}=3\\x-\dfrac{2}{5}=-3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{17}{5}\\x=-\dfrac{13}{5}\end{matrix}\right.\)

b: Ta có: \(\dfrac{21}{5}+3:\left|\dfrac{x}{4}-\dfrac{2}{3}\right|=6\)

\(\Leftrightarrow3:\left|\dfrac{1}{4}x-\dfrac{2}{3}\right|=6-\dfrac{21}{5}=\dfrac{9}{5}\)

\(\Leftrightarrow\left|\dfrac{1}{4}x-\dfrac{2}{3}\right|=\dfrac{5}{3}\)

\(\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{4}x-\dfrac{2}{3}=\dfrac{5}{3}\\\dfrac{1}{4}x-\dfrac{2}{3}=-\dfrac{5}{3}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\dfrac{1}{4}x=\dfrac{7}{3}\\\dfrac{1}{4}x=-1\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=\dfrac{28}{3}\\x=-4\end{matrix}\right.\)

`a)2sqrt{48}-4sqrt{27}+sqrt{75}+sqrt{12}`

`=8sqrt3-12sqrt3+5sqrt3+2sqrt3`

`=3sqrt3`

`b)sqrt{(3-sqrt5)^2}-sqrt{20}`

`=3-sqrt5-2sqrt5`

`=3-3sqrt5`

2 câu cuối không rõ đề :v

(2/5)^2+5 1/3*(4,5-2)+23/-4

=4/25+16/3*2,5+(-23/4)

=4/25+40/3+(-23/4)

=203/15+(-23/4)

=467/60

a)4⁵*3²+2¹⁰*30=2¹⁰*9+2¹⁰*30=2¹⁰*(9+30)=2¹⁰*39

b) 37-x/3=x-13/7

37+13/7=x+x/3

272/7=4x/3

x=272/7:4/3

x=204/7

Câu c là 2/5+1-4/5=

5-1/3-4/5=58/15

2-3/5-4/5=3/5

2+1-4/5=11/5

a, 2x+ 1/4 = 3/2

2x = 3/2-1/4

2x = 5/4

x=5/4:2

x= 5/8 

b, (x-5) - 1/3 = 2/5

x-5= 2/5+1/3

x-5=11/15

x=11/15+5

x=86/15

c, (4,5-2x):3/4=4/3

(4,5-2x)=4/3. 3/4

4,5-2x=1

2x= 5,5

x=5,5:2

x=2,75

a) 2x+1/4=3/2

=> 2x      =3/2-1/4

=> 2x       =5/4

=> x         =5/4:2

=> x         =5/8

b) (x-5)-1/3=2/5

=>  x-5      =2/5+1/3

=> x-5        =11/15

=> x           =11/15+5

=> x           =86/15

c) (4,5-2x):3/4=4/3

=> 4,5-2x       =4/3x3/4

=> 4,5-2x       =1

=>   2x          =4,5-1

=>   2x           =3,5

=>    x             =3,5:2

=>    x             =1,75