1,

a) 3,2x +(-12)x +2,7=-4,9 b)-5,6x+2,9x-3,86=-9,8

=>3,2x+(-12)x=-4,9-2,7 =>-5,6x+2,9x=-9,8+3,86

=>3,2x+(-12)x=-7,6 =>-5,6x+2,9x=-5,94

=>x[3,2+(-12)]=-7,6 =>x[(-5,6)+2,9]=-5,94

=>2x=-7,6=>x=-7,6:2=-3,8 =>-2,7x=-5,94=>x=(-5,94):(-2,7)=2,2

Nhầm môn r bạn ơi

\(A=-5,13:\left(5\dfrac{5}{28}-1\dfrac{8}{9}.1,25+1\dfrac{16}{63}\right)\)

\(=-5,13:\left(5\dfrac{5}{28}-2\dfrac{13}{36}+1\dfrac{16}{63}\right)\)

\(=5,13:\left[\left(5-2+1\right)+\left(\dfrac{5}{28}-\dfrac{13}{36}+\dfrac{16}{63}\right)\right]\)

\(=5,13:\left(4+\dfrac{1}{14}\right)\)

\(=1,26\)

`A=-5,13:(5 5/28-1 8/9 .1,25+1 16/63)`

`A=-513/100:(145/28-17/9 .5/4+79/63)`

`A=-513/100:(145/28-85/36+79/63)`

`A=-513/100:(355/126+79/63)`

`A=-513/100:57/14`

`A=-63/50`

\(A=-5,13:\left(5\dfrac{5}{28}-1\dfrac{8}{9}.1,25+1\dfrac{16}{63}\right)\)

\(A=-5,13:\left[\left(5-2+1\right)+\left(\dfrac{5}{28}-\dfrac{18}{36}+\dfrac{16}{63}\right)\right]\)

\(A=-5,13:\left(4+\dfrac{1}{14}\right)\)

\(A=-5,13:\left(\dfrac{56}{14}+\dfrac{1}{14}\right)\)

\(A=-5,13:\dfrac{57}{14}\)

\(A=\dfrac{-513}{100}:\dfrac{57}{14}\)

\(A=\dfrac{-513}{100}\times\dfrac{14}{57}\)

\(A=\dfrac{-63}{50}\)

a) \(A=-5,13:\left(5\dfrac{5}{28}-1\dfrac{8}{9}.1,25+1\dfrac{16}{63}\right)\)

\(\Leftrightarrow A=-5,13:\left(5\dfrac{5}{28}-\dfrac{85}{36}+1\dfrac{16}{63}\right)\)

\(\Leftrightarrow A=-5,13:\left(\dfrac{355}{126}+1\dfrac{16}{63}\right)\)

\(\Leftrightarrow A=-5,13:\dfrac{57}{14}\)

\(\Leftrightarrow A=\dfrac{-63}{50}\)

b) \(B=\left(3\dfrac{1}{3}.1,9+19,5:4\dfrac{1}{3}\right).\left(\dfrac{62}{75}-\dfrac{4}{25}\right)\)

\(\Leftrightarrow B=\left(\dfrac{19}{3}+19,5.\dfrac{3}{13}\right).\dfrac{2}{3}\)

\(\Leftrightarrow B=\left(\dfrac{19}{3}+\dfrac{9}{2}\right).\dfrac{2}{3}\)

\(\Leftrightarrow B=\dfrac{65}{6}.\dfrac{2}{3}\)

\(\Leftrightarrow B=\dfrac{65}{9}\)

\(a,\left(7+3\dfrac{1}{4}-\dfrac{3}{5}\right)+\left(0,4-5\right)-\left(4\dfrac{1}{4}-1\right)\)

\(=\left(7+\dfrac{13}{4}-\dfrac{3}{5}\right)-\dfrac{23}{5}-\left(\dfrac{17}{4}-1\right)\)

\(=7+\dfrac{13}{4}-\dfrac{3}{5}-\dfrac{23}{5}-\dfrac{17}{4}+1\)

\(=\left(7+1\right)+\left(\dfrac{13}{4}-\dfrac{17}{4}\right)-\left(\dfrac{3}{5}+\dfrac{23}{5}\right)\)

\(=8-\dfrac{4}{4}-\dfrac{26}{5}\)

\(=7-\dfrac{26}{5}\)

\(=\dfrac{9}{5}\)

\(b,\dfrac{2}{3}-\left[\left(-\dfrac{7}{4}\right)-\left(\dfrac{1}{2}+\dfrac{3}{8}\right)\right]\)

\(=\dfrac{2}{3}-\left(-\dfrac{7}{4}-\dfrac{1}{2}-\dfrac{3}{8}\right)\)

\(=\dfrac{2}{3}-\left(-\dfrac{14}{8}-\dfrac{4}{8}-\dfrac{3}{8}\right)\)

\(=\dfrac{2}{3}-\left(-\dfrac{21}{8}\right)\)

\(=\dfrac{2}{3}+\dfrac{21}{8}\)

\(=\dfrac{79}{24}\)

\(c,\left(9-\dfrac{1}{2}-\dfrac{3}{4}\right):\left(7-\dfrac{1}{4}-\dfrac{5}{8}\right)\)

\(=\left(\dfrac{36}{4}-\dfrac{2}{4}-\dfrac{3}{4}\right):\left(\dfrac{56}{8}-\dfrac{2}{8}-\dfrac{5}{8}\right)\)

\(=\dfrac{31}{4}:\dfrac{49}{8}\)

\(=\dfrac{62}{49}\)

\(d,3-\dfrac{1-\dfrac{1}{7}}{1+\dfrac{1}{7}}=3-\dfrac{\dfrac{7}{7}-\dfrac{1}{7}}{\dfrac{7}{7}+\dfrac{1}{7}}=3-\left(\dfrac{6}{7}:\dfrac{8}{7}\right)=3-\dfrac{3}{4}=\dfrac{9}{4}\)