$a.(x²+27)(x+9)-(x+3)³$
$=x³+9x²+27x+243-(x³+9x²+27x+27)$
$=x³+9x²+27x+243-x³-9x²-27x-27$
$=243-27=216$
$b.(x-1)³-(x+1)³-6(x+1)(x-1)$
$=x³-3x²+3x-1-(x³+3x²+3x+1)-6(x²-1)$
$=x³-3x²+3x-1-x³-3x²-3x-1-6x²+6$
$=-12x²+4$
$=-4(3x²-1)$
Mk xin 5sao,trả lời hay nhất nha,chỗ nào chưa hiểu thì hỏi mk tiếp nhé,mk trả lời hết