document.write( "Question 888262: Numbers a, b and c are such that a ≥ 0, b ≥ 0 and c ≥ 0. Prove:
\n" ); document.write( "2(a^3+b^3+c^3 )≥ab(a+b)+bc(b+c)+ca(c+a)
\n" ); document.write( "
\n" ); document.write( "

Algebra.Com's Answer #537274 by Edwin McCravy(20055)\"\" \"About 
You can put this solution on YOUR website!
To prove:\r\n" );
document.write( "\"a%5E3%2Bb%5E3%2Bc%5E3\"\"%22%22%3E=%22%22\"\"ab%28a%2Bb%29%2Bbc%28b%2Bc%29%2Bca%28c%2Ba%29\"\r\n" );
document.write( "\r\n" );
document.write( "By Cauchy's inequality, the arithmetic mean of any number of \r\n" );
document.write( "positive numbers is greater than or equal to the geometric mean.\r\n" );
document.write( "\r\n" );
document.write( "Let's take two of the cubes to be the same.\r\n" );
document.write( "The arithmetic mean of \"a%5E3\",\"a%5E3\", and \"b%5E3\" is greater\r\n" );
document.write( "than or equal to the geometric mean of those cubes, two of which are the same.\r\n" );
document.write( "\r\n" );
document.write( "\"%28a%5E3%2Ba%5E3%2Bb%5E3%29%2F3\"\"%22%22%3E=%22%22\"\"root%283%2Ca%5E3a%5E3b%5E3%29\"\r\n" );
document.write( "\"%282a%5E3%2Bb%5E3%29%2F3\"\"%22%22%3E=%22%22\"\"root%283%2Ca%5E6b%5E3%29\"\r\n" );
document.write( "\"%282a%5E3%2Bb%5E3%29%2F3\"\"%22%22%3E=%22%22\"\"a%5E2b%29\"\r\n" );
document.write( "\"2a%5E3%2Bb%5E3\"\"%22%22%3E=%22%22\"\"3a%5E2b%29\"\r\n" );
document.write( "\r\n" );
document.write( "By symmetry we can also prove that\r\n" );
document.write( "\r\n" );
document.write( "\"2a%5E3%2Bc%5E3\"\"%22%22%3E=%22%22\"\"3a%5E2c%29\"\r\n" );
document.write( "\"2b%5E3%2Ba%5E3\"\"%22%22%3E=%22%22\"\"3b%5E2a%29\"\r\n" );
document.write( "\"2b%5E3%2Bc%5E3\"\"%22%22%3E=%22%22\"\"3b%5E2c%29\"\r\n" );
document.write( "\"2c%5E3%2Ba%5E3\"\"%22%22%3E=%22%22\"\"3c%5E2a%29\"\r\n" );
document.write( "\"2c%5E3%2Bb%5E3\"\"%22%22%3E=%22%22\"\"3c%5E2b%29\"\r\n" );
document.write( "\r\n" );
document.write( "Add all 6 inequalities:\r\n" );
document.write( "\r\n" );
document.write( "\"6a%5E3%2B6b%5E3%2B6c%5E3\"\"%22%22%3E=%22%22\"\"3a%5E2b%2B3a%5E2c%2B3b%5E2a%2B3b%5E2c%2B3c%5E2a%2B3c%5E2b\"\r\n" );
document.write( "\r\n" );
document.write( "Divide through by 3\r\n" );
document.write( "\r\n" );
document.write( "\"2a%5E3%2B2b%5E3%2B2c%5E3\"\"%22%22%3E=%22%22\"\"a%5E2b%2Ba%5E2c%2Bb%5E2a%2Bb%5E2c%2Bc%5E2a%2Bc%5E2b\"\r\n" );
document.write( "\r\n" );
document.write( "Factor out 2 on the left.\r\n" );
document.write( "Rearrange the terms on the right so we can factor \r\n" );
document.write( "pairwise and get the given desired right side: \r\n" );
document.write( "\r\n" );
document.write( "\"2%28a%5E3%2Bb%5E3%2Bc%5E3%29\"\"%22%22%3E=%22%22\"\"a%5E2b%2Bb%5E2a%2Bb%5E2c%2Bc%5E2b%2Bc%5E2a%2Ba%5E2c\"\r\n" );
document.write( "\r\n" );
document.write( "On the right, factor the 1st two, middle two and last two terms:\r\n" );
document.write( "\r\n" );
document.write( "\"2%28a%5E3%2Bb%5E3%2Bc%5E3%29\"\"%22%22%3E=%22%22\"\"ab%28a%2Bb%29%2Bbc%28b%2Bc%29%2Bca%28c%2Ba%29\" \r\n" );
document.write( "\r\n" );
document.write( "Edwin
\n" ); document.write( "
\n" );