If two internal straight-lines are constructed on one of the sides of a triangle, from its ends, the constructed (straight-lines) will be less than the two remaining  sides of the triangle, but will encompass a greater angle. For let the two internal straight-lines $BD$ and $DC$ have been constructed on one of the sides $BC$ of the triangle $ABC$, from its ends $B$ and $C$ (respectively). I say that  $BD$ and $DC$ are less than the (sum of the) two  remaining sides of the triangle $BA$ and $AC$, but encompass an angle $BDC$ greater than $BAC$.    <prf>  Thus, $BDC$ is much greater than $BAC$.Thus, if two internal straight-lines are constructed on one of the sides of a triangle, from its ends,  the constructed (straight-lines) are less than the two remaining  sides of the triangle, but  encompass a greater angle.