a, `( (-3)/4 + 2/5 ) : 3/7 + ( 3/5 + (-1)/4 ) : 3/7`
`= [ ( (-3)/4 +2 /5 ) + ( 3/5 + (-1)/4 ) ]: 3/7`
`= [ ( (-3)/4 + (-1)/4 ) + ( 2 /5 + 3/5 ) . 7/3`
`= ( -1 + 1 ) . 7/3`
`= 0 . 7/3`
`= 0`
b, `7/8 : ( 2/9 - 1/18 ) + 7/8 : ( 1/16 - 5/12 )`
`= 7/8 : [ ( 2/9 - 1/18 ) + ( 1/16 - 5/12 ) ]`
`= 7/8 : [ ( 4/18 - 1/18 ) + ( 3/48 - 20/48 ) ]`
`= 7/8 : [ 1/6 + ( -17 )/48 ]`
`= 7/8 : [ 8/48 - 17/48 ]`
`= 7/8 : (-9)/48`
`= 7/8 . (-48)/9`
`= (-14)/3`
$\text{HỌC TỐT NHA ~}$
$\text{#NOCOPY}$
`#Sâu`
