Đáp án:
`123. 8 \sqrt{x} - 3 \sqrt{4/81} = 5,2`
`⇒ 8 \sqrt{x} - 2/3 = 5,2`
`⇒ 8 \sqrt{x} = 88/15`
`⇒ \sqrt{x} = 11/15`
`⇒ x = 121/225`
`124. 2/5 - 2 \sqrt{x} = 7/5 + \sqrt{1/9}`
`⇒ 2/5 - 2 \sqrt{x} = 68/45`
`⇒ 2 \sqrt{x} = (-10)/9`
`⇒ \sqrt{x} = (-5)/9`
`⇒ x = ∅`
`125. 12 - 3x^2 = 10 + \sqrt{25/16}`
`⇒ 12 - 3x^2 = 45/4`
`⇒ 3x^2 = 3/4`
`⇒ x^2 = 1/4`
`⇒ x^2 = (±1/2)^2`
`⇒ x = ±1/2`
`126. 3/4 + 0,5 (\sqrt{11}/2)^2 = 2,5x^2 + 4`
`⇒ 3/4 + 11/8 = 2,5x^2 + 4`
`⇒ 17/8 = 2,5x^2 + 4`
`⇒ 2,5x^2 = -15/8`
`⇒ x^2 = -3/4`
`⇒ x = ∅`
`127. 5x : 3/5 = 4/7 : \sqrt{4/49}`
`⇒ 5x : 3/5 = 2`
`⇒ 5x = 6/5`
`⇒ x = 6/25`
`128. 0,15 : 3 \sqrt{x} = 0,3 : 2/3`
`⇒ 0,15 : 3 \sqrt{x} = 9/20`
`⇒ 3 \sqrt{x} = 1/3`
`⇒ \sqrt{x} = 1/9`
`⇒ x = 1/3`
