Question 105828
{{{r=(L-O)/(L+O)}}}
{{{(L+O)*r=cross(L+O)*(L-O)/cross((L+O))}}} Multiply both sides by {{{(L+O)}}}
{{{Lr+Or=L-O}}} Distribute and simplify. 
Get all L terms on one side, everything else on the other. 
{{{Lr+Or-L=L-L-O}}} Additive inverse of L. 
{{{Lr-L+Or=-O}}}
{{{Lr-L+Or-Or=-O-Or}}}Additive inverse of Or. 
{{{L*(r-1)=-O(r+1)}}} Distributive property.
{{{L*(r-1)/(r-1)=-O(r+1)/(r-1)}}}Multiplicative inverse of (r-1).
{{{L=-O(r+1)/(r-1)}}}
{{{L=O*((1+r)/(1-r))}}}