` ( 2x xx 3/5) ^2 - 9/25 = 0`
`(2x xx 3/5)^2 = 0 + 9/25`
`(2x xx 3/5)^2 = 9/25`
`=> (2x xx 3/5 ) ^2 = (±3/5)^2 `
`=> 2x xx 3/5 = 3/5`
`=> 2x = 3/5 : 3/5`
`2x = 3/5 xx 5/3`
`2x = 1`
`x = 1 : 2`
`x = 1/2`
`=> 2x xx 3/5 = (-3)/(5)`
`2x = (-3)/5 : 3/5`
`2x= -1`
`x=-1:2`
`x=-1/2`
Vậy ` x ∈ { 1/2; -1/2}`