L
luc876


cho a,b,c,d>0
TM: $abc+bcd+cda+dab=a+b+c+d+ \sqrt{2012}$
CMR: $(a^2+1)(b^2+1)(c^2+1)(d^2+1) \ge 2012$
TM: $abc+bcd+cda+dab=a+b+c+d+ \sqrt{2012}$
CMR: $(a^2+1)(b^2+1)(c^2+1)(d^2+1) \ge 2012$
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