Subtangent and Subnormal

Given a curve, the subtangent at a point  
\[(x,y)\]
  on the curve is the interval on the  
\[x\]
  axis between  
\[x\]
  and the intercept  
\[x_T\]
  of the tangent with the  
\[x\]
  axis, and the subnormal is the interval on the  
\[x\]
  axis between  
\[x\]
  and the intercept of the normal with the axis.