Hướng dẫn trả lời:
4) `21/13x = -7/26`
`→ x = -7/26 ÷ 21/13`
`→ x = -7/26cdot13/21`
`→ x = -1/6`
Vậy `x = -1/6`
5) `x ÷ (-4/21) = 2 4/5`
`→ x ÷ (-4/21) = 14/5`
`→ x = 14/5 cdot (-4/21)`
`→ x = -8/15`
Vậy `x = -8/15`
6) `x ÷ (-4 2/7) = - 4 1/5`
`→ x ÷ (-30/7) = - 21/5`
`→ x = - 21/5 cdot (-30/7)`
`→ x = 18`
Vậy `x = 18`
7) `x ÷ 5/7 = 3/10`
`→ x = 3/10 cdot 5/7`
`→ x = 3/14`
Vậy `x = 3/14`
8) `x ÷ 2 3/8 = 1 2/5`
`→ x ÷ 19/8 = 7/5`
`→ x = 7/5 cdot 19/8`
`→ x = 133/40`
Vậy `x = 133/40`
9) `({2x}/5 - 1) ÷ (-5) = 1/4`
`→ {2x}/5 - 1 = 1/4 cdot (-5)`
`→ {2x}/5 - 1 = -5/4`
`→ {2x}/5 = -5/4 + 1`
`→ {2x}/5 = -5/4 + 4/4`
`→ {2x}/5 = -1/4`
`→ 2x = -1/4cdot5`
`→ 2x = -5/4`
`→ x = -5/4 ÷ 2`
`→ x = -5/4 cdot 1/2`
`→ x = -5/8`
Vậy `x = -5/8`
10) `(3 1/4 ÷ x)cdot(-1 1/4) = - 5/3 - 5/6`
`→ (13/4 ÷ x)cdot(-5/4) = - 30/18 - 15/18`
`→ (13/4 ÷ x)cdot(-5/4) = - 45/18`
`→ (13/4 ÷ x)cdot(-5/4) = - 5/2`
`→ 13/4 ÷ x = - 5/2 ÷ (-5/4)`
`→ 13/4 ÷ x = - 5/2 cdot (-4/5)`
`→ 13/4 ÷ x = 2`
`→ x = 13/4 ÷ 2`
`→ x = 13/4 cdot 1/2`
`→ x = 13/8`
Vậy `x = 13/8`
11) `(- 1 1/5 + x) ÷ (-3 3/5) = -7/4 + 1/4 ÷ 1/8`
`→ (- 6/5 + x) ÷ (-18/5) = -7/4 + 1/4 cdot 8/1`
`→ (- 6/5 + x) ÷ (-18/5) = -7/4 + 8/4`
`→ (- 6/5 + x) ÷ (-18/5) = 1/4`
`→ - 6/5 + x = 1/4 cdot (-18/5)`
`→ - 6/5 + x = -9/10`
`→ x = -9/10 - (- 6/5)`
`→ x = -9/10 + 6/5`
`→ x = -9/10 + 12/10`
`→ x = 3/10`
Vậy `x = 3/10`
