a)(x+a)(x+b)(x+c)
=($x^{2}$+ax+bx+ab)(x+c)
=$x^{3}$+a$x^{2}$+b$x^{2}$+abx+c$x^{2}$+acx+bcx+abc
=$x^{3}$+(a+b+c)$x^{2}$+(ab+bc+ca)x+abc
b)$a^{2}$ (b-c) + $b^{2}$(c-a) + $c^{2}$(b-a)
= $a^{2}$b - $a^{2}$c + $b^{2}$c -$b^{2}$a +$c^{2}$a - $c^{2}$b
= ab(a-b) - c($a^{2}$ - $b^{2}$) + $c^{2}$(a-b)
=(a-b)[ab-c(a+b)+$c^{2}$]
=ab(ab-ac-bc+$c^{2}$)
=ab[a(b-c)-c(b-c)]
=(a-b)(b-c)(a-c)
CHO MÌNH 5* NHA
