Tính và rút gọn nếu có thể A) 3/5-(-7/4) B) -8/18- (-15/27) C) -3/29-16/58 D) 8/40-(-36/45) E) -(-1/21)-1/28 F) 1/-8-(-5/9) P) -18/24-15/21 làm nhanh

Đáp án:

$a)$ $\dfrac{3}{5}-\left(-\dfrac{7}{4}\right)$ $=\dfrac{47}{20}$

$b)$ $-\dfrac{8}{18}-\left(-\dfrac{15}{27}\right)$ $=\dfrac{1}{9}$

$c)$ $\dfrac{-3}{29}-\dfrac{16}{58}$ $=-\dfrac{11}{29}$

$d)$ $\dfrac{8}{40}-\left(-\dfrac{36}{45}\right)$ $=1$

$e)$ $-\left(\dfrac{-1}{21}\right)-\dfrac{1}{28}$ $=\dfrac{1}{84}$

$f)$ $\dfrac{1}{-8}-\left(-\dfrac{5}{9}\right)$ $=\dfrac{31}{72}$

$p)$ ` -18/24-15/21` $=-\dfrac{41}{28}$

Giải thích các bước giải:

$a)$ $\dfrac{3}{5}-\left(-\dfrac{7}{4}\right)$

$=\dfrac{3}{5}+\dfrac{7}{4}$

$=\dfrac{12}{20}+\dfrac{35}{20}$

$=\dfrac{12+35}{20}$

$=\dfrac{47}{20}$

$b)$ $-\dfrac{8}{18}-\left(-\dfrac{15}{27}\right)$

$=-\dfrac{4}{9}+\dfrac{5}{9}$

$=\dfrac{-4+5}{9}$

$=\dfrac{1}{9}$

$c)$ $\dfrac{-3}{29}-\dfrac{16}{58}$

$=-\dfrac{3}{29}-\dfrac{8}{29}$

$=\dfrac{-3-8}{29}$

$=-\dfrac{11}{29}$

$d)$ $\dfrac{8}{40}-\left(-\dfrac{36}{45}\right)$

$=\dfrac{8}{40}+\dfrac{36}{45}$

$=\dfrac{1}{5}+\dfrac{4}{5}$

$=\dfrac{1+4}{5}$

$=\dfrac{5}{5}$

$=1$

$e)$ $-\left(\dfrac{-1}{21}\right)-\dfrac{1}{28}$

$=\dfrac{1}{21}-\dfrac{1}{28}$

$=\dfrac{4}{84}-\dfrac{3}{84}$

$=\dfrac{4-3}{84}$

$=\dfrac{1}{84}$

$f)$ $\dfrac{1}{-8}-\left(-\dfrac{5}{9}\right)$

$=-\dfrac{1}{8}+\dfrac{5}{9}$

$=-\dfrac{9}{72}+\dfrac{40}{72}$

$=\dfrac{-9+40}{72}$

$=\dfrac{31}{72}$

$p)$ ` -18/24-15/21`

$=-\dfrac{3}{4}-\dfrac{5}{7}$

$=-\dfrac{21}{28}-\dfrac{20}{28}$

$=\dfrac{-21-20}{28}$

$=-\dfrac{41}{28}$