Đáp án:
a)$\dfrac{61}{30}$
b.$\dfrac{-29}{60}$
Giải thích các bước giải:
a)Ta có:
$(\dfrac{-2}{-5}+\dfrac{-5}{-6})+\dfrac45$
$=\left(\dfrac{2}{5}+\dfrac{5}{6}\right)+\dfrac{4}{5}$
$=\left(\dfrac{12}{30}+\dfrac{25}{30}\right)+\dfrac{4}{5}$
$=\dfrac{12+25}{30}+\dfrac{4}{5}$
$=\dfrac{37}{30}+\dfrac{4}{5}$
$=\dfrac{37}{30}+\dfrac{24}{30}$
$=\dfrac{37+24}{30}$
$=\dfrac{61}{30}$
Ta có:
$(\dfrac{-2}{-5}+\dfrac{-5}{-6})+\dfrac45$
$=\left(\dfrac{2}{5}+\dfrac{5}{6}\right)+\dfrac{4}{5}$
$=\dfrac{2}{5}+\dfrac{5}{6}+\dfrac{4}{5}$
$=\dfrac25+\dfrac45+\dfrac56$
$=\dfrac{2+4}5+\dfrac56$
$=\dfrac65+\dfrac56$
$=\dfrac{36}{30}+\dfrac{25}{30}$
$=\dfrac{36+25}{30}$
$=\dfrac{61}{30}$
b.Ta có:
$\dfrac{-3}{-4}+(\dfrac{11}{-15}+\dfrac{-1}{2})$
$=\dfrac{3}{4}+(\dfrac{-11}{15}+\dfrac{-1}{2})$
$=\dfrac{3}{4}+(\dfrac{-22}{30}+\dfrac{-15}{30})$
$=\dfrac{3}{4}+\dfrac{-22-15}{30}$
$=\dfrac{3}{4}+\dfrac{-37}{30}$
$=\dfrac{3}{4}-\dfrac{37}{30}$
$=\dfrac{45}{60}-\dfrac{74}{60}$
$=\dfrac{45-74}{60}$
$=\dfrac{-29}{60}$
Ta có:
$\dfrac{-3}{-4}+(\dfrac{11}{-15}+\dfrac{-1}{2})$
$=\dfrac{3}{4}-\dfrac{11}{15}-\dfrac{1}{2}$
$=\dfrac{45}{60}-\dfrac{44}{60}-\dfrac{30}{60}$
$=\dfrac{45-44-30}{60}$
$=\dfrac{-29}{60}$
