a: \(\Leftrightarrow\left(x-\dfrac{2}{5}\right):\dfrac{3}{2}=-\dfrac{5}{4}+\dfrac{5}{2}=\dfrac{5}{4}\)

\(\Leftrightarrow x-\dfrac{2}{5}=\dfrac{5}{4}\cdot\dfrac{3}{2}=\dfrac{15}{8}\)

hay x=91/40

b: \(\Leftrightarrow\left(2.5x-3.6\right)=-1\cdot\dfrac{12}{7}=\dfrac{-12}{7}\)

=>2,5x=66/35

hay x=132/175

c: \(\Leftrightarrow\left(\dfrac{15}{4}-2x\right)=\dfrac{19}{9}:\dfrac{4}{3}=\dfrac{19}{9}\cdot\dfrac{3}{4}=\dfrac{19}{12}\)

=>2x=15/4-19/12=45/12-19/12=26/12

=>x=13/12

1) \(A=\left|-3,75\right|-\frac{31}{2}+\frac{1}{4}\)

\(A=\frac{15}{4}-\frac{31}{2}+\frac{1}{4}\)

\(A=\left(-\frac{47}{4}\right)+\frac{1}{4}\)

\(A=-\frac{23}{2}.\)

2) \(A=\frac{3}{2}-\left(-3\right)-\left(2,5-3\right)-\left[1,5+\left(-2,5\right)\right]\)

\(A=\frac{3}{2}-\left(-3\right)-\left(-\frac{1}{2}\right)-\left(-1\right)\)

\(A=\frac{9}{2}-\left(-\frac{1}{2}\right)-\left(-1\right)\)

\(A=5-\left(-1\right)\)

\(A=6.\)

Chúc bạn học tốt!

1) \(A=\left|-3.75\right|-\frac{31}{2}+\frac{1}{4}\)

\(\Leftrightarrow A=3.75-\frac{62}{4}+\frac{1}{4}\)

\(\Leftrightarrow A=\frac{15}{4}-\frac{62}{4}+\frac{1}{4}\)

\(\Leftrightarrow A=\frac{15-62+1}{4}\)

\(\Leftrightarrow A=-\frac{46}{4}=-\frac{23}{2}\)

Vậy : \(A=-\frac{23}{2}\)

2) \(A=\frac{3}{2}-\left(-3\right)-\left(2,5-3\right)-\left[1,5+\left(-2,5\right)\right]\)

\(\Leftrightarrow A=\frac{3}{2}+3-\left(-0,5\right)-\left(-1\right)\)

\(\Leftrightarrow A=1,5+3+0,5+1\)

\(\Leftrightarrow A=6\)

Vậy : \(A=6\)

   \(4\frac{1}{2}:\left(2,5-\frac{33}{4}\right)+\left(-\frac{1}{2}\right)^2\)

= \(\frac{9}{2}:\left(-\frac{23}{4}\right)+\frac{1}{4}\)

= \(-\frac{18}{23}+\frac{1}{4}\)

= \(-\frac{49}{92}\)

   4 1/2 : ( 2,5 - 3 3/4 ) + -1/2^2

= 4 1/2 : ( 2,5 - 15/4 ) + - 1/2

= 9/2 : -5/4 + -1/2

= -18/5 + -1/2

= -41/10 

= - 4,1.

`(2/3-0,25+2)-(2-5/2+1/4)-(2,5-1/3)`

`= 2/3 -1/4 +2-2+ 5/2 -1/4 -5/2 +1/3`

`= (2/3 +1/3) +(-1/4 -1/4) + (2-2) + (5/2-5/2)`

`= 3/3 + (-1/2) + 0 + 0`

`= 1 +(-1/2)`

`= 1/2`

\(\left(\dfrac{2}{3}-0,25+2\right)-\left(2-\dfrac{5}{2}+\dfrac{1}{4}\right)-\left(2,5-\dfrac{1}{3}\right)\\ =\dfrac{2}{3}-0,25+2-2+\dfrac{5}{2}-\dfrac{1}{4}-2,5+\dfrac{1}{3}\\ =\left(\dfrac{2}{3}+\dfrac{1}{3}\right)+\left(\dfrac{5}{2}-2,5\right)+\left(2-2\right)+\left(-\dfrac{1}{4}-0,25\right)\\ =\dfrac{3}{3}+\left(2,5-2,5\right)+0+\left(-\dfrac{1}{4}-\dfrac{1}{4}\right)\\ =1+0+0+\left(-\dfrac{1}{2}\right)=\dfrac{1}{2}\)

\(\left(\dfrac{2}{3}-0,5+2\right)-\left(2-\dfrac{5}{2}+\dfrac{1}{4}\right)-\left(2,5-\dfrac{1}{3}\right)\)

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

\(=\left(\dfrac{1}{6}+2\right)-\left(\dfrac{-1}{2}+\dfrac{1}{4}\right)-\dfrac{13}{6}\)

\(=\dfrac{13}{6}+\dfrac{1}{4}-\dfrac{13}{6}=\dfrac{1}{4}\)

1, 

\(\begin{array}{l}2,5.\left( {4,1 - 3 - 2,5 + 2.7,2} \right) + 4,2:2\\ = 2,5.\left( {4,1 - 3 - 2,5 + 14,4} \right) + 4,2:2\\ = 2,5.\left( {1,1 - 2,5 + 14,4} \right) + 2,1\\ = 2,5.\left( { - 1,4 + 14,4} \right) + 2,1\\ = 2,5.13 + 2,1\\ = 32,5 + 2,1\\ = 34,6\end{array}\)

2, 

Cách 1:

\(\begin{array}{l}2,86.4 + 3,14.4 - 6,01.5 + {3^2}\\ = 11,44 + 12,56 - 30,05 + 9\\ = \left( {11,44 + 12,56} \right) + \left( { - 30,05 + 9} \right)\\ = 24 + \left( { - 21,05} \right)\\ = 24 - 21,05\\ = 2,95\end{array}\)

Cách 2: 

\(\begin{array}{l}2,86.4 + 3,14.4 - 6,01.5 + {3^2}\\ = 4.(2,86+3,14) - 30,05 + 9\\ = 4.6 + \left( { - 30,05 + 9} \right)\\ = 24 + \left( { - 21,05} \right)\\ = 24 - 21,05\\ = 2,95\end{array}\)