Figure 3 Parametric line formulas

a) Vector form

  X(t) = X1 + (X2 - X1)t
b) Scalar form

  x(t) = x1 + (x2 - x1)t
  y(t) = y1 + (y2 - y1)t
c) Iterative form

  X(t) = X1 + (X2 - X1)(t)
  X(t + dt) = X1 + (X2 -X1)(t + dt)
= X1 + (X2 - X1)t + (X2 - X1)dt
= X(t) + (X2 - X1)dt, X(0) = X1