Tính theo cách hợp lí:
a/ 4/20+16/42+ 6/15+ -3/5 +2/21+ -10/21+3/20
b/ 42/46+ 250/186+ -2121/2323+ -125125/143143
Tính theo cách hợp lí:
a/ 4/20+16/42+ 6/15+ -3/5 +2/21+ -10/21+3/20
b/ 42/46+ 250/186+ -2121/2323+ -125125/143143
Dáp án + giải thích bước giải :
`a) 4/20 + 16/42 + 6/15 + (-3)/5 + 2/21 + (-10)/21 + 3/20`
`= (4/20 + (-3)/5 + 6/15 + 3/20) + (16/42 + 2/21 + (-10)/21)`
`= 3/20 + 0`
`= 3/20`
`b) 42/46 + 250/186 + (-2121)/2323 + (-125125)/143143`
`= 21/23 + 125/93 + (-21)/23 + (-125)/43`
`= (21/23 + (-21)/23) + (125/93 + (-125)/43)`
`= 0 + 6250/13299`
`= 6250/13299`
Đáp án+Giải thích các bước giải:
$\\a)\dfrac{4}{20}+\dfrac{16}{42}+\dfrac{6}{15}+\dfrac{-3}{5}+\dfrac{2}{21}+\dfrac{-10}{21}+\dfrac{3}{20}\\=\left(\dfrac{4}{20}+\dfrac{-3}{5}+\dfrac{6}{15}+\dfrac{3}{20}\right)+\left(\dfrac{16}{42}+\dfrac{2}{21}+\dfrac{-10}{21}\right)\\=\left(\dfrac{4}{20}+\dfrac{-12}{20}+\dfrac{8}{20}+\dfrac{3}{20}\right)+\left(\dfrac{8}{21}+\dfrac{2}{21}+\dfrac{-10}{21}\right)\\=\dfrac{3}{20}$
$\\b)\dfrac{42}{46}+ \dfrac{250}{186}+ \dfrac{-2121}{2323}+ \dfrac{-125125}{143143}\\=\dfrac{21}{23}+ \dfrac{125}{93}+ \dfrac{-21}{23}+ \dfrac{-125}{143}\\=\left(\dfrac{21}{23}+\dfrac{-21}{23}\right)+\left(\dfrac{125}{93}+ \dfrac{-125}{143}\right)\\=\dfrac{6250}{13299}$