`d) (x - 5)^4 = (x - 5)^6`
`(x - 5)^4 - (x - 5)^6 = 0`
`(x - 5)^4 - (x - 5)^4 . (x - 5)^2 = 0`
`(x - 5)^4 . [1 - (x - 5)^2] = 0`
`⇒ (x - 5)^4 = 0 hoặc 1 - (x - 5)^2 = 0`
`TH1:`
`(x - 5)^4 = 0`
`x - 5 = 0`
`x = 5`
`TH2:`
`1 - (x - 5)^2 = 0`
`(x - 5)^2 = 1`
`x - 5 = 1`
`x = 6`
`Vậy: x ∈ {5; 6}`