`text(Ta có :)`
`(a + b + c)^2 = 0`
`⇒ a^2 + b^2 + c^2 + 2ab + 2bc + 2ac = 0`
`⇒ 2ab + 2bc + 2ac = -1`
`⇒ (ab + bc + ca)^2 = -1/2`
`⇒ (ab + bc + ca)^2 = 1/4`
`⇒ a^2b^2 + b^2c^2 + c^2a^2 + 2abc(a + b + c) = 1/4`
`⇒ a^2b^2 + b^2c^2 + c^2a^2 = 1/4`
`text(Lại có : )`
`(a^2 + b^2 + c^2) = 1`
`⇒ (a^2 + b^2 + c^2)^2 = 1`
`⇒ a^4 + b^4 + c^4 + 2a^b^2 + 2b^2c^2 + 2c^2a^2 = 1`
`⇒ a^4 + b^4 + c^4 + 2( a^2b^2 + b^2c^2 + c^2a^2) = 1`
`⇒ a^4 + b^4 + c^4 + 2 . 1/4 = 1`
`⇒ a^4 + b^4 + c^4 = 1 - 1/2 = 1/2`
