Đáp án:
Giải thích các bước giải:
Bài 2:
$a,x+\dfrac{1}{3}=\dfrac{2}{5}-\left (\dfrac{-1}{3} \right )$
$⇔x+\dfrac{1}{3}=\dfrac{2}{5}+\dfrac{1}{3}$
$⇔x+\dfrac{1}{3}=\dfrac{11}{15}$
$⇔x=\dfrac{11}{15}-\dfrac{1}{3}$
$⇔x=\dfrac{6}{15}=\dfrac{2}{5}$
$b.\dfrac{3}{7}-x=\dfrac{1}{4}-\left (-\dfrac{3}{5} \right )$
$⇔\dfrac{3}{7}-x=\dfrac{1}{4}+\dfrac{3}{5}$
$⇔\dfrac{3}{7}-x=\dfrac{17}{20}$
$⇔x=\dfrac{3}{7}-\dfrac{17}{20}$
$⇔x=\dfrac{-59}{140}$
Bài 3:
$B=\left (-\dfrac{5}{9} \right ).\dfrac{3}{11}+\left (-\dfrac{13}{18} \right ).\dfrac{3}{11}$
$B=\dfrac{3}{11}.\left (-\dfrac{5}{9}-\dfrac{13}{18} \right )$
$B=\dfrac{3}{11}.\left (\dfrac{-23}{18} \right )$
$B=\dfrac{-23}{66}$
$\text{Vậy chọn đáp án : $C$.}$
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