X=ab(a+b)+bc(b+c)+ca(c+a)+2abc
=a2b+ab2+b2c+bc2+c2a+a2c+2abc
=b(a+c)2+b2(a+c)+ac(a+c)+2abc
=[b(a+c)+b2+ac](a+c)+2abc
=(ab+bc+b2+ac)(a+c)+2abc
=[b(c+b)+a(b+c)](a+c)+2abc
=[(b+a)(b+c)](a+c)+2abc
rồi j nữa, tịt rồi
X=ab(a+b)+bc(b+c)+ca(c+a)+2abc
=a2b+ab2+b2c+bc2+ac2+a2c+2abc
=a(ab+b2+c2+ac+2bc)+bc(b+c)
=a[(b+c)2+a(b+c)]+bc(b+c)
=a(b+c)(b+c+a)+bc(b+c)
=a(b+c)(a+b+c+bc)
Xin hết
X=ab(a+b)+bc(b+c)+ca(c+a)+2abc
= a2b+ab2+b2c+bc2+ac2+a2c+2abc
= a(ab+b2+c2+ac+2bc)+bc(b+c)
=a[a(b+c)+(b+c)2 ] +bc(b+c)
=a(a+b+c)(b+c)+ bc(b+c)
=(b+c) (a2+ab+ac+bc)
=(b+c) (a+b)(b+c)