Ta Có: (a^2+1)(b^2+1)(c^2+1)
= (a^2+ab+bc+ ca)(b^2+ab+bc+ ca)(c^2+ab+bc+ ca)
=[(a^2 +ab)+(bc+ ca)][(b^2 +ab)+(bc+ ca)][(c^2 +ab)+(bc+ ca)]
=(a+c)(a+b)(a+b)(b+c)(c+a)(b+c)
=[(a+c)(a+b)(b+c)]^2
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