Đáp án`+`Giải thích các bước giải:
` a. x + 2/3 = 4/5`
`- >x = 4/5 - 2/3 = (4.3)/(5.3) - (2.5)/(3.5) =12/15 - 10/15 = 2/15 `
` b. x - 2/7 = 7/21 `
`-> x= 7/21 + 2/7 = 7/21 + (2.3)/(7.3) = 7/21 + 6/21 = 13/21 `
` c. -x - 3/4 = -8/11 `
`-> -x = -8/11 + 3/4 = (-8.4)/(11.4) + (3.11)/(4.11) = -32/44 + 33/44 = 1/44 `
`-> x =-1/44 `
` d. 11/12 - (2/5 +x) = 2/3 `
`-> 2/5 + x = 11/12 - 2/3 = 11/12 - (2.4)/(3.4) = 11/12 - 8/12 = 3/12 = 1/4 `
`-> x = 1/4 - 2/5 = (1.5)/(4.5) - (2.4)/(5.4) = 5/20 - 8/20 = -3/20 `