Question 973590
A whole circle would have a circumference of 
{{{C=2pi*R}}}
So half a circle would be 
{{{C[sc]=pi*R}}}
{{{C[sc]=(pi/2)*D}}}
Then the line to connect the two endpoints would have a length equal to the diameter.
So the total length would be,
{{{L=(pi/2)*D+D}}}
{{{L=((pi/2)+1)D}}}
So if {{{L=1}}},
{{{D=1/(pi/2+1)}}}
{{{D=2/(pi+2)}}}{{{m}}}