Đáp án: Mik làm 3 bài lun nhá @@
Bài 2 :
$a) A= (\dfrac{1}{3} -\dfrac{8}{15} -\dfrac{1}{7}) +(\dfrac{2}{3} +\dfrac{-7}{15} +1\dfrac{1}{7})$
$ = (\dfrac{1}{3} +\dfrac{2}{3}) + (-\dfrac{8}{15} +\dfrac{-7}{15}) +(-\dfrac{1}{7} +1\dfrac{1}{7})$
$ = 1 -1 +1$
$= 1$
$b)B = 0,25 + \dfrac{3}{5} - (\dfrac{1}{8} - \dfrac{2}{5} + 1\dfrac{1}{4})$
$ = 0,25 + \dfrac{3}{5} - \dfrac{1}{8} +\dfrac{2}{5} -\dfrac{5}{4}$
$ = (0,25 - \dfrac{5}{4}) + (\dfrac{3}{5}+\dfrac{2}{5}) -\dfrac{1}{8}$
$ = -1 +1 -\dfrac{1}{8}$
$ =-\dfrac{1}{8}$
Bài 3 :
$\dfrac{1}{2} -\dfrac{2}{3}+ \dfrac{3}{4} -\dfrac{4}{5} +\dfrac{5}{6}-\dfrac{6}{7} +\dfrac{7}{8} +\dfrac{6}{7} -\dfrac{5}{6} + \dfrac{4}{5} -\dfrac{3}{4} +\dfrac{2}{3} -\dfrac{1}{2})$
$ = (\dfrac{1}{2} -\dfrac{1}{2}) + (-\dfrac{2}{3} +\dfrac{2}{3}) + (\dfrac{3}{4} -\dfrac{3}{4}) +(\dfrac{4}{5} -\dfrac{4}{5}) + (\dfrac{5}{6} -\dfrac{5}{6}) + (\dfrac{6}{7} -\dfrac{6}{7}) + \dfrac{7}{8}$
$ = 0 + 0 +0+0+0+0 + \dfrac{7}{8}$
$= \dfrac{7}{8}$
Bài 4 :
$a) x-\dfrac{1}{5} = \dfrac{3}{2} +\dfrac{1}{6}$
$ ⇔ x - \dfrac{1}{5} = \dfrac{5}{3}$
$⇔ x = \dfrac{5}{3} +\dfrac{1}{5}$
$⇔x = \dfrac{28}{15}$
Vậy $x=\dfrac{28}{15}$
$b) \dfrac{4}{5} - (-\dfrac{1}{8}) = \dfrac{7}{8} -x$
$ ⇔ \dfrac{37}{40} = \dfrac{7}{8} -x$
$⇔ \dfrac{37}{40} -\dfrac{7}{8} = -x$
$⇔\dfrac{1}{20} = -x$
$⇔x= -\dfrac{1}{20}$
Vậy $x=-\dfrac{1}{20}$
$c) -1,25 +\dfrac{2}{15} -x=2$
$⇔-x = 2 +1,25 -\dfrac{2}{15}$
$⇔ -x = \dfrac{187}{60}$
$⇔ x= -\dfrac{187}{60}$
Vậy $x=-\dfrac{187}{60}$
$d)2\dfrac{1}{2} -x + \dfrac{4}{5} = \dfrac{2}{3}-(-\dfrac{4}{7})$
$⇔\dfrac{5}{2} -x + \dfrac{4}{5} = \dfrac{2}{3} +\dfrac{4}{7}$
$⇔ -x=\dfrac{2}{3} +\dfrac{4}{7} -\dfrac{4}{5} -\dfrac{5}{2}$
$⇔ -x= -\dfrac{433}{210}$
$⇔ x=\dfrac{433}{210}$
Vậy $x=\dfrac{433}{210}$
