Hướng dẫn trả lời:
a) `1/4 + 3/4x = 3/4.`
`→ 3/4x = 3/4 - 1/4.`
`→ 3/4x = 2/4.`
`→ 3/4x = 1/2.`
`→ x = 1/2 ÷ 3/4.`
`→ x = 1/2. 4/3.`
`→ x = 2/3.`
Vậy `x = 2/3.`
b) `x.(1/4 + 1/5) - (1/7 + 1/8) = 0.`
`→ x.(5/20 + 4/20) - (8/56 + 7/56) = 0.`
`→ 9/20x - 15/56 = 0.`
`→ 9/20x = 15/56.`
`→ x = 15/56 ÷ 9/20.`
`→ x = 15/56. 20/9.`
`→ x = 25/42.`
Vậy `x = 25/42.`
Đáp án:
a) `x = 2/3.`
b) `x = 25/42.`