a) `a³+b³+c³-3ab`
`= a³+b³+c³+3a²b+3ab²-3a²b-3ab²-3ab`
` = (a+b)³+c³-3ab(a+b+c)`
`= (a+b+c)(a²+2ab+b²-ac-bc+c²)-3ab(a+b+c)`
`= (a+b+c)(a²+b²+c²-ab-ac-bc)`
b) `(x-y)³+(y-z)³+(z-x)³`
`= x³-3x²y+3xy²-y³+y³-3y²z+3yz²-z³+z³-3x²z+3xz²-x³
`= -3x²y+3xy²-3y²z+3yz²-3x²z+3xz²`
`= 3(x-z)( x-y)(z-y)`
