Example 17 Given that a,b,c are all positive numbers, and satisfy abc=1. Prove: a3(b+c)1+b3(c+a)1+c3(a+b)1⩾23.
Solution
Analysis: The original inequality is equivalent to a(b+c)b2c2+b(c+a)c2a2+c(a+b)a2b2⩾23. When a=b=c=1, equality holds, at which point a(b+c)b2c2=4a(b+c),b(c+a)c2a2=4b(c+a),c(a+b)a2b2=4c(a+b), and a(b+c)b2c2+4a(b+c)⩾bc,b(c+a)c2a2+4b(c+a)⩾ca,c(a+b)a2b2+4c(a+b)⩾ab. Adding the last three inequalities side by side yields a(b+c)b2c2+b(c+a)c2a2+c(a+b)a2b2⩾21(ab+bc+ca)⩾233(abc)2=23.
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