bc^2+ca^2+ab^2-cb^2-ac^2-ba^2
=a^2(c-b)+a(b^2-c^2)+bc(c-b)
=(c-b)(a^2-ab-ac+bc)
=(c-b)(a-b)(a-c)
因为a>b>c
∴c-b0
a-c>0
∴(c-b)(a-b)(a-c)