cho a,b,c,d$\geq$0, a+b+c+d=4. cm:
$(1+a^4)(1+b^4)(1+c^4)(1+d^4)\geqslant (1+a^3)(1+b^3)(1+c^3)(1+d^3)$
$(1+a^4)(1+b^4)(1+c^4)(1+d^4)\geqslant (1+a^3)(1+b^3)(1+c^3)(1+d^3)$
Started By phancuong123, 30-08-2013 - 22:38
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