Re: HSC 2016 2U Marathon
$\noindent Let any ordered set of 3 consecutive terms in the sequence be $a,b,c$
b-a=c-b\\ b=\frac { a+c }{ 2 } \\ \\ \frac { b }{ a } =\frac { c }{ b } \\ \\ { b }^{ 2 }=ac\\ \\ \\ \therefore \frac { { (a+c) }^{ 2 } }{ 4 } =ac\\ \\ { (a-c) }^{ 2 }=0\\ a=c\\ \\...