Question 316667
{{{(x-y)/ (1/x-1/y)=(xy(x-y))/ (xy(1/x-1/y))}}}
{{{(x-y)/ (1/x-1/y)=(xy(x-y))/ (y-x)}}}
{{{(x-y)/ (1/x-1/y)=-(xy(x-y))/ (x-y)}}}
{{{(x-y)/ (1/x-1/y)=-(xy*cross((x-y)))/cross((x-y))}}}
{{{(x-y)/ (1/x-1/y)=-xy}}}