Re: HSC 2013 4U Marathon
Alternatively,
a^2+b^2 \geq 2ab
$We need to sub into a and b, all the combinations of 2 numbers from the set$ \ \ x_1, \ x_2, \ x_2 \ \dots, \ x_n
x_1^2+x_1^2 \geq 2x_1 x_2
x_1^2+x_3^2 \geq 2x_1x_3
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.
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x_1^2+x_n^2 \geq 2x_1x_n
x_2^2+x_3^2 \geq 2x_2 x_3...