Mathcad 15 , Symbolic Evaluate ?

• Your "Minimize" command is only minimizing the function f which calculates the distance from O to P. You should not be surprised that the result is the point P (or a point close to it within the set numerical precision)
  If you want the other yellow equations seen as constraints you have to create a solve block by adding "Given" in front of it.
  Furthermore its advisable to decrease the value of CTOL
• The functions of @ttokoro you try to use to draw the arc are not suitable for real Mathcad. Mathcad does not provide the row selector which ttokoro used (you can't just replace it for the column selector as you did) and Mathcads 3D plot does not accept NaN's in the data values.
  Furthermore in the other thread ttokoro used 101 point for the linePS, you are only creating 11 points. So obviously you can't use a loop from 0 to 101!
  The programs for PSline and Cline have to be rewritten to suit the specifics of Mathcad which are different from Prime. 
  And although the 3D plot in Prime is extremely poor and far inferior to that in Mathcad, the ability to use NaN's and also the simpler data structure to plot a curve is a significant improvement over Mathcad (as is the introduction of the row selector).
  Conclusion: PTC did an incredible amount wrong, but not everything 😉

BTW, as already mentioned in the other thread - ttkoros way to plot the arc will fail if the arc angle is equal to or greater than 180 degree. Furthermore the points created to represent the arc are not equally spaced - points in the middle of the arc are farther apart. Using enough points can hide that effect efficiently, though.