Đáp án:
`2a³+2b³+2c³-6abc`
Giải thích các bước giải:
`(a+b)³+(b+c)³+(c+a)³-3(a+b)(b+c)(c+a)`
`=a³+3a²b+3ab²+b³+b³+3b²c+3bc²+c³+c³+3ac²+3a²c+a³-3[(a+b)(b+c)](c+a)`
`=a³+3a²b+3ab²+b³+b³+3b²c+3bc²+c³+c³+3ac²+3ac²+a³-3(ab+ac+b²+bc)(c+a)`
`=a³+3a²b+3ab²+b³+b³+3b²c+3bc²+c³+c³+3ac²+3a²c+a³-3(abc+a²b+ac²+a²c+b²c+ab²+bc²+abc)````=a³+3a²b+3ab²+b³+b³+3b²c+3bc²+c³+c³+3ac²+3a²c+a³-3abc-3a²b-3ac²-3a²c-3b²c-3ab²-3bc²-3abc`
`=(a³+a³)+(3a²b-3a²b)+(3ab²-3ab²)+(b³+b³)+(3b²c-3b²c)+(3bc²-3bc²)+(c³+c³)+(3ac²-3ac²)+(3a²c-3a²c)-(3abc+3abc)`
`=2a³+2b³+2c³-6abc`
