Scaling a Line

I have a theoretical line within a script with the start point of the line, the end point of the line, the slope, and the length of the line all stored in variables. How do I change the length of the line so that the end point and the length are matched up. Currently, I am doing this:

 public Vector3 ScaleLine(float newLength){
     Vector3 Result = new Vector3 (Position1.x, Position1.y, Position1.z);
     Result.x = ((Position2.x - Position1.x)/Length) * newLength + Position1.x;
     Result.z = ((Position2.z - Position1.z)/Length) * newLength + Position1.z;
     return Result;
 }

and I am running it through a script to find the angle between to points:

 Vector3.Angle(wallLines[wallLines.Count - 1].Position1, line.ScaleLine(wallLines[wallLines.Count - 1].Length));

However, the angle is displayed incorrectly, and I think its due to the scale of the line being off.