Moving Points in X/Y axis within grasshopper

Hi Guys,

I am trying to build a definition that replicates a cobra's ribs opening up and forming a hood when it's pissed off. I'm starting by creating a control point curve between two points(see Below). I want to move point 1 across to the left, whilst maintaining the length of the curve. So the curve basically straightens out. I don't really know where to start in moving the point. Any help would be really appreciated. Thanks

Phil