`A=((√x)/(2+√x)+(x+4)/(4-x)):((2√x+1)/(x-2√x)-1/(√x))`
`=(√x(2-√x)+x+4)/(4-x):(2√x+1-(√x-2))/(√x(√x-2))`
`=(2(2+√x))/(4-x).(√x(√x-2))/(√x+3)`
`=(2√x)/(√x+3)`
`A=(2√x)/(√x+3)=-1/3`
`⇔(2√x)/(√x+3)+1/3=0`
`⇔6√x+√x+3=0`
`⇔7√x+3=0`
`⇒` vô nghiệm
`(a√a+b√b)/(√a+√b)-√a√b=((√a+√b)(a+b-√a√b)/(√a+√b)-√a√b`
`=a+b-2√a√b`
`=(√a-√b)^2`