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20 16 champion of national mathematics league.
∫a+b+c = 5,a? +b? +c? = 15,

∴2(ab+bc+ac)=(a+b+c)? -(a? +b? +c? )=5? -15= 10, that is AB+BC+AC = 5;

∵a? +b? +c? -3abc=(a+b+c)(a? +b? +c? -ab-bc-ac),

∴47-3abc=5×( 15-5)=50, that is, ABC =-1;

There's an a +ab+b? =a? +ab+ac+ab+b? +BC-a B- BC-AC =(a+b)(a+b+c)-(a b+ BC+AC)=(5-c)5-5 = 5(4-c);

Similarly, there is a B? +bc+c? =5(4-b),a? +ac+c? = 5(4-c);

Then the original formula =5×5×5(4-a)(4-b)(4-c).

= 12564- 16(a+b+c)+4(a b+ BC+AC)-ABC

= 12564- 16×5+4×5-(- 1)

=625.

Ask for adoption o(≧v≦)o~~